## Publications of Shailesh Chandrasekharan    :chronological  alphabetical  combined listing:

%% Books
@book{fds16196,
Author = {S. Chandrasekharan and U.-J. Wiese},
Title = {AN INTRODUCTION TO CHIRAL SYMMETRY ON THE
LATTICE},
Booktitle = {Prog. Part. Nucl. Phys. Vol. 53, issue 1,},
Year = {2004},
Key = {fds16196}
}

@book{fds4128,
Author = {S. Chandrasekharan},
Title = {NOVEL QUANTUM MONTE CARLO ALGORITHMS FOR
FERMIONS},
Booktitle = {Quantum Monte Carlo: Recent Advances and Common Problems in
Condensed Matter Physics and Field Theory},
Publisher = {EDIZIONI ETS},
Editor = {M. Compostrini and M.P. Lomardo and F. Paderiva},
Year = {2001},
Abstract = {Recent research shows that the partition function for a
class of models involving fermions can be written as a
statistical mechanics of clusters with positive definite
weights. This new representation of the model allows one to
construct novel algorithms. We illustrate this through
models consisting of fermions with and without spin. A
Hubbard type model with both attractive and repulsive
interactions becomes tractable using the new approach.
Precision results in the two dimensional attractive model
confirm a superfluid phase transition in the
Kosterlitz-Thouless universality class.},
Key = {fds4128}
}

@book{fds4130,
Author = {S. Chandrasekharan},
Title = {SOLVING SIGN PROBLEMS WITH MERON ALGORITHMS},
Series = {Springer Proc. Phys. 86, pp 28-42},
Booktitle = {Computer Simulations in Condensed Matter Physics
XIII},
Publisher = {Springer},
Editor = {D.P. Landau and S.P.Lewis and H.-B.Shuttler},
Year = {2000},
Month = {January},
Key = {fds4130}
}

@article{Chandrasekharan:1994kx,
Author = {Chandrasekharan, S.},
Title = {CRITICAL BEHAVIOR AT THE QCD PHASE TRANSITION WITH TWO
MASSLESS QUARK FLAVORS},
Booktitle = {Continuous Advances in QCD},
Publisher = {World Scientific},
Editor = {Smilga, A.V.},
Year = {1994},
Key = {Chandrasekharan:1994kx}
}

@book{fds4165,
Author = {S. Chandrasekharan},
Title = {CRITICAL BEHAVIOR AT THE QCD PHASE TRANSITION WITH TWO
MASSLESS QUARK FLAVORS},
Booktitle = {Continuous Advances in QCD},
Publisher = {World Scientific},
Editor = {Andrei V. Smilga},
Year = {1994},
Key = {fds4165}
}

%% Papers Published
@article{fds333670,
Author = {Ayyar, V and Chandrasekharan, S and Rantaharju,
J},
Title = {Benchmark results in the 2D lattice Thirring model with a
chemical potential},
Journal = {Physical Review D},
Volume = {97},
Number = {5},
Year = {2018},
Month = {March},
url = {http://dx.doi.org/10.1103/PhysRevD.97.055041},
Abstract = {© 2018 authors. We study the two-dimensional lattice
Thirring model in the presence of a fermion chemical
potential. Our model is asymptotically free and contains
massive fermions that mimic a baryon and light bosons that
mimic pions. Hence, it is a useful toy model for QCD,
especially since it, too, suffers from a sign problem in the
auxiliary field formulation in the presence of a fermion
chemical potential. In this work, we formulate the model in
both the world line and fermion-bag representations and show
that the sign problem can be completely eliminated with open
boundary conditions when the fermions are massless. Hence,
we are able accurately compute a variety of interesting
quantities in the model, and these results could provide
benchmarks for other methods that are being developed to
solve the sign problem in QCD.},
Doi = {10.1103/PhysRevD.97.055041},
Key = {fds333670}
}

@article{fds332870,
Author = {Banerjee, D and Chandrasekharan, S and Orlando,
D},
Title = {Conformal Dimensions via Large Charge Expansion.},
Journal = {Physical Review Letters},
Volume = {120},
Number = {6},
Pages = {061603},
Year = {2018},
Month = {February},
url = {http://dx.doi.org/10.1103/physrevlett.120.061603},
Abstract = {We construct an efficient Monte Carlo algorithm that
overcomes the severe signal-to-noise ratio problems and
helps us to accurately compute the conformal dimensions of
large-Q fields at the Wilson-Fisher fixed point in the O(2)
universality class. Using it, we verify a recent proposal
that conformal dimensions of strongly coupled conformal
field theories with a global U(1) charge can be obtained via
a series expansion in the inverse charge 1/Q. We find that
the conformal dimensions of the lowest operator with a fixed
charge Q are almost entirely determined by the first few
terms in the series.},
Doi = {10.1103/physrevlett.120.061603},
Key = {fds332870}
}

@article{fds331599,
Author = {Chandrasekharan, S and Ayyar, V},
Title = {Generating a nonperturbative mass gap using Feynman diagrams
in an asymptotically free theory},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {96},
Publisher = {American Physical Society},
Year = {2017},
Month = {December},
url = {http://dx.doi.org/10.1103/PhysRevD.96.114506},
Doi = {10.1103/PhysRevD.96.114506},
Key = {fds331599}
}

@article{fds331600,
Author = {Ayyar, V and Chandrasekharan, S},
Title = {Generating a nonperturbative mass gap using Feynman diagrams
in an asymptotically free theory},
Journal = {Physical Review D},
Volume = {96},
Number = {11},
Year = {2017},
Month = {December},
url = {http://dx.doi.org/10.1103/PhysRevD.96.114506},
Abstract = {© 2017 American Physical Society. Using the example of a
two-dimensional four-fermion lattice field theory we
demonstrate that Feynman diagrams can generate a mass gap
when massless fermions interact via a marginally relevant
coupling. We introduce an infrared cutoff through the finite
system size so that the perturbation series for the
partition function and observables become convergent. We
then use the Monte Carlo approach to sample sufficiently
high orders of diagrams to expose the presence of a mass gap
in the lattice model.},
Doi = {10.1103/PhysRevD.96.114506},
Key = {fds331600}
}

@article{fds331601,
Author = {Huffman, E and Chandrasekharan, S},
Title = {Fermion bag approach to Hamiltonian lattice field theories
in continuous time},
Journal = {Physical Review D},
Volume = {96},
Number = {11},
Year = {2017},
Month = {December},
url = {http://dx.doi.org/10.1103/PhysRevD.96.114502},
Abstract = {© 2017 American Physical Society. We extend the idea of
fermion bags to Hamiltonian lattice field theories in the
continuous time formulation. Using a class of models we
argue that the temperature is a parameter that splits the
fermion dynamics into small spatial regions that can be used
to identify fermion bags. Using this idea we construct a
continuous time quantum Monte Carlo algorithm and compute
critical exponents in the 3d Ising Gross-Neveu universality
class using a single flavor of massless Hamiltonian
staggered fermions. We find η=0.54(6) and ν=0.88(2) using
lattices up to N=2304 sites. We argue that even sizes up to
N=10,000 sites should be accessible with supercomputers
available today.},
Doi = {10.1103/PhysRevD.96.114502},
Key = {fds331601}
}

@article{fds323235,
Author = {Hann, CT and Huffman, E and Chandrasekharan, S},
Title = {Solution to the sign problem in a frustrated quantum
impurity model},
Journal = {Annals of Physics},
Volume = {376},
Pages = {63-75},
Year = {2017},
Month = {January},
url = {http://dx.doi.org/10.1016/j.aop.2016.11.006},
Doi = {10.1016/j.aop.2016.11.006},
Key = {fds323235}
}

@article{fds323133,
Author = {Huffman, E and Chandrasekharan, S},
Title = {Solution to sign problems in models of interacting fermions
and quantum spins.},
Journal = {Physical review. E},
Volume = {94},
Number = {4-1},
Pages = {043311},
Year = {2016},
Month = {October},
url = {http://dx.doi.org/10.1103/physreve.94.043311},
Abstract = {We show that solutions to fermion sign problems that are
found in the formulation where the path integral is expanded
in powers of the interaction in continuous time can be
extended to systems involving fermions interacting with
dynamical quantum spins. While these sign problems seem
unsolvable in the auxiliary field approach, solutions emerge
in the world-line representation of quantum spins. Combining
this idea with meron-cluster methods, we are able to further
extend the class of models that are solvable. We demonstrate
these solutions to sign problems by considering several
examples of strongly correlated systems that contain the
physics of semimetals, insulators, superfluidity, and
antiferromagnetism.},
Doi = {10.1103/physreve.94.043311},
Key = {fds323133}
}

@article{fds323134,
Author = {Ayyar, V and Chandrasekharan, S},
Title = {Fermion masses through four-fermion condensates},
Journal = {The Journal of High Energy Physics},
Volume = {2016},
Number = {10},
Year = {2016},
Month = {October},
url = {http://dx.doi.org/10.1007/JHEP10(2016)058},
Doi = {10.1007/JHEP10(2016)058},
Key = {fds323134}
}

@article{fds323135,
Author = {Huffman, E and Banerjee, D and Chandrasekharan, S and Wiese,
U-J},
Title = {Real-time evolution of strongly coupled fermions driven by
dissipation},
Journal = {Annals of Physics},
Volume = {372},
Pages = {309-319},
Year = {2016},
Month = {September},
url = {http://dx.doi.org/10.1016/j.aop.2016.05.019},
Doi = {10.1016/j.aop.2016.05.019},
Key = {fds323135}
}

@article{fds323136,
Author = {Ayyar, V and Chandrasekharan, S},
Title = {Origin of fermion masses without spontaneous symmetry
breaking},
Journal = {Physical Review D},
Volume = {93},
Number = {8},
Year = {2016},
Month = {April},
url = {http://dx.doi.org/10.1103/PhysRevD.93.081701},
Doi = {10.1103/PhysRevD.93.081701},
Key = {fds323136}
}

@article{fds327863,
Author = {Chandrasekharan, S},
Title = {Fermion bags, topology and index theorems},
Journal = {PoS - Proceedings of Science},
Volume = {Part F128557},
Year = {2016},
Month = {January},
formulation helps to extend the concepts of topology and
index theorem associated with non-Abelian gauge theories to
simple lattice fermion field theories. Using this extension
we can argue that fermion masses can arise either through
the traditional mechanism where some lattice symmetry of the
action that forbids fermion mass terms is explicitly,
anomalously, or spontaneously broken, or through a
non-traditional mechanism where all lattice symmetries
continue to be preserved. We provide examples of simple
fermion lattice field theories for each of these scenarios
of fermion mass generation.},
Key = {fds327863}
}

@article{fds245667,
Author = {Ayyar, V and Chandrasekharan, S},
Title = {Massive fermions without fermion bilinear
condensates},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {91},
Number = {6},
Year = {2015},
Month = {March},
ISSN = {1550-7998},
url = {http://dx.doi.org/10.1103/PhysRevD.91.065035},
Doi = {10.1103/PhysRevD.91.065035},
Key = {fds245667}
}

@article{fds245668,
Author = {Zou, H and Liu, Y and Lai, C-Y and Unmuth-Yockey, J and Yang, L-P and Bazavov, A and Xie, ZY and Xiang, T and Chandrasekharan, S and Tsai,
S-W and Meurice, Y},
Title = {Progress towards quantum simulating the classical
model},
Journal = {Physical Review A - Atomic, Molecular, and Optical
Physics},
Volume = {90},
Number = {6},
Year = {2014},
Month = {December},
ISSN = {1050-2947},
url = {http://dx.doi.org/10.1103/PhysRevA.90.063603},
Doi = {10.1103/PhysRevA.90.063603},
Key = {fds245668}
}

@article{fds303638,
Author = {Huffman, E and Chandrasekharan, S},
Title = {Solution to new sign problems with Hamiltonian Lattice
Fermions},
Journal = {PoS (LATTICE 2014) 058},
Year = {2014},
Month = {November},
url = {http://arxiv.org/abs/1411.7147v2},
Abstract = {We present a solution to the sign problem in a class of
particle-hole symmetric Hamiltonian lattice fermion models
on bipartite lattices using the idea of fermion bags. The
solution remains valid when the particle-hole symmetry is
broken through a staggered chemical potential term. This
solution allows, for the first time, simulations of some
massless four-fermion models with minimal fermion doubling
and with an odd number of fermion flavors using ultra-local
actions. One can thus study a variety of quantum phase
transitions that have remained unexplored so far due to sign
problems.},
Key = {fds303638}
}

@article{fds225570,
Author = {E.F. Huffman and S. Chandrasekharan},
Title = {Solution to sign problems in half-filled spin-polarized
electronic systems},
Journal = {Phys. Rev. (Rapid Communications)},
Volume = {B89},
Pages = {111101},
Year = {2014},
Month = {February},
url = {http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.111101},
Abstract = {http://journals.aps.org/prb/abstract/10.1103/PhysRevB.89.111101},
Doi = {10.1103/PhysRevB.89.111101},
Key = {fds225570}
}

@article{fds303639,
Author = {Huffman, EF and Chandrasekharan, S},
Title = {Solution to sign problems in half-filled spin-polarized
electronic systems},
Journal = {Phys. Rev. B},
Volume = {89},
Pages = {111101},
Year = {2013},
Month = {October},
url = {http://arxiv.org/abs/1311.0034v1},
Abstract = {We solve the sign problem in a particle-hole symmetric
spin-polarized fermion model on bipartite lattices using the
idea of fermion bags. The solution can be extended to a
class of models at half filling but without particle-hole
symmetry. Attractive Hubbard models with an odd number of
fermion species can also be solved. The new solutions should
allow us to study quantum phase transitions that have
remained unexplored so far due to sign problems.},
Doi = {10.1103/PhysRevB.89.111101},
Key = {fds303639}
}

@article{fds303640,
Author = {Chandrasekharan, S and Li, A},
Title = {Quantum critical behavior in three dimensional lattice
Gross-Neveu models},
Volume = {88},
Pages = {021701},
Year = {2013},
Month = {April},
url = {http://arxiv.org/abs/1304.7761v1},
Abstract = {We study quantum critical behavior in three dimensional
lattice Gross-Neveu models containing two massless Dirac
fermions. We focus on two models with SU(2) flavor symmetry
and either a $Z_2$ or a U(1) chiral symmetry. Both models
could not be studied earlier due to sign problems. We use
the fermion bag approach which is free of sign problems and
compute critical exponents at the phase transitions. We
estimate $\nu = 0.83(1)$, $\eta = 0.62(1)$, $\eta_\psi = 0.38(1)$ in the $Z_2$ and $\nu = 0.849(8)$, $\eta = 0.633(8)$, $\eta_\psi = 0.373(3)$ in the U(1)
model.},
Doi = {10.1103/PhysRevD.88.021701},
Key = {fds303640}
}

@article{fds303641,
Author = {Chandrasekharan, S},
Title = {Fermion Bag Approach to Fermion Sign Problems},
Volume = {49},
Pages = {90},
Year = {2013},
Month = {April},
url = {http://arxiv.org/abs/1304.4900v1},
Abstract = {The fermion bag approach is a new method to tackle fermion
sign problems in lattice field theories. Using this approach
it is possible to solve a class of sign problems that seem
unsolvable by traditional methods. The new solutions emerge
when partition functions are written in terms of fermion
bags and bosonic worldlines. In these new variables it is
possible to identify hidden pairing mechanisms which lead to
the solutions. The new solutions allow us for the first time
to use Monte Carlo methods to solve a variety of interesting
lattice field theories, thus creating new opportunities for
understanding strongly correlated fermion
systems.},
Doi = {10.1140/epja/i2013-13090-y},
Key = {fds303641}
}

@article{fds323137,
Author = {Chandrasekharan, S},
Title = {Quantum critical behavior with massless staggered fermions
in three dimensions},
Journal = {PoS - Proceedings of Science},
Volume = {29-July-2013},
Pages = {049},
Year = {2013},
Month = {January},
Abstract = {We report on studies of quantum critical behavior in three
dimensional lattice Gross-Neveu models with one flavor of
staggered fermions. We focus on two models, one with
SU(2)×Z2 symmetry and the other with an SU(2)×U(1)
symmetry. Both these models could not be studied earlier
with conventional Monte Carlo methods due to sign problems.
However, the fermion bag approach is free of sign problems
for these models and allows us to compute the critical
exponents at the quantum phase transition that separates the
massless fermion phase at small couplings and the massive
fermion phase at large couplings. Our results help resolve
some old puzzles in the field.},
Key = {fds323137}
}

@article{PosLattice2012,
Author = {Chandrasekharan Shailesh},
Title = {Fermion Bag Solutions to Sign Problems},
Journal = {Proceedings of Science},
Volume = {Lattice2012},
Pages = {224},
Year = {2012},
Month = {December},
Key = {PosLattice2012}
}

@article{PhysRevLett.108.140404,
Author = {Chandrasekharan, S and Li, A},
Title = {Fermion bags, duality, and the three dimensional massless
lattice thirring model.},
Journal = {Physical Review Letters},
Volume = {108},
Number = {14},
Pages = {140404},
Publisher = {American Physical Society},
Year = {2012},
Month = {April},
url = {http://www.ncbi.nlm.nih.gov/pubmed/22540775},
Abstract = {The recently proposed fermion-bag approach is a powerful
technique to solve some four-fermion lattice field theories.
Because of the existence of a duality between strong and
weak couplings, the approach leads to efficient Monte Carlo
algorithms in both these limits. The new method allows us
for the first time to accurately compute quantities close to
the quantum critical point in the three dimensional lattice
Thirring model with massless fermions on large lattices. The
critical exponents at the quantum critical point are found
to be ν=0.85(1), η=0.65(1), and η(ψ)=0.37(1).},
Doi = {10.1103/PhysRevLett.108.140404},
Key = {PhysRevLett.108.140404}
}

@article{PhysRevD.85.091502,
Author = {Chandrasekharan, S and Li, A},
Title = {Fermion bag solutions to some sign problems in four-fermion
field theories},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {85},
Number = {9},
Pages = {091502},
Publisher = {American Physical Society},
Year = {2012},
ISSN = {1550-7998},
Abstract = {Lattice four-fermion models containing N flavors of
staggered fermions, which are invariant under Z 2 and U(1)
chiral symmetries, are known to suffer from sign problems
when formulated using the auxiliary field approach. Although
these problems have been ignored in previous studies, they
can be severe. Here we show that the sign problems disappear
when the models are formulated in the fermion bag approach,
allowing us to solve them rigorously for the first time. ©
2012 American Physical Society.},
Doi = {10.1103/PhysRevD.85.091502},
Key = {PhysRevD.85.091502}
}

@article{PhysRevD.86.021701,
Author = {Chandrasekharan, S},
Title = {Solutions to sign problems in lattice Yukawa
models},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {86},
Number = {2},
Pages = {021701},
Publisher = {American Physical Society},
Year = {2012},
ISSN = {1550-7998},
Abstract = {We prove that sign problems in the traditional approach to
some lattice Yukawa models can be completely solved when
fermions are formulated using fermion bags and bosons are
formulated in the worldline representation. We prove this
within the context of two examples of three-dimensional
models, symmetric under U L(1)×U R(1)×Z 2(parity)
transformations, one involving staggered fermions and the
other involving Wilson fermions. We argue that these models
have interesting quantum phase transitions that can now be
studied using Monte Carlo methods. © 2012 American Physical
Society.},
Doi = {10.1103/PhysRevD.86.021701},
Key = {PhysRevD.86.021701}
}

@article{fds303646,
Author = {Chandrasekharan, S and Li, A},
Title = {The generalized fermion-bag approach},
Volume = {Lattice 2011},
Pages = {058},
Year = {2011},
Month = {November},
url = {http://arxiv.org/abs/1111.5276v1},
Abstract = {We present a new approach to some four-fermion lattice field
theories which we call the generalized fermion bag approach.
The basic idea is to identify unpaired fermionic degrees of
freedom that cause sign problems and collect them in a bag.
Paired fermions usually act like bosons and do not lead to
sign problems. A resummation of all unpaired fermion degrees
of freedom inside the bag is sufficient to solve the fermion
sign problem in a variety of interesting cases. Using a
concept of duality we then argue that the size of the
fermion bags is small both at strong and weak couplings.
This allows us to construct efficient algorithms in both
these limits. Using the fermion bag approach, we study the
quantum phase transition of the 3D massless lattice
Thirrring model which is of interest in the context of
Graphene. Using our method we are able to solve the model on
lattices as large as $40^3$ with moderate computational
resources. We obtain the precise location of the quantum
critical point and the values of the critical exponents
through this study.},
Key = {fds303646}
}

@article{fds303643,
Author = {Chandrasekharan, S and Wiese, U-J},
Title = {Partition Functions of Strongly Correlated Electron Systems
as "Fermionants"},
Year = {2011},
Month = {August},
url = {http://arxiv.org/abs/1108.2461v1},
Abstract = {We introduce a new mathematical object, the "fermionant"
${\mathrm{Ferm}}_N(G)$, of type $N$ of an $n \times n$
matrix $G$. It represents certain $n$-point functions
involving $N$ species of free fermions. When N=1, the
fermionant reduces to the determinant. The partition
function of the repulsive Hubbard model, of geometrically
frustrated quantum antiferromagnets, and of Kondo lattice
models can be expressed as fermionants of type N=2, which
naturally incorporates infinite on-site repulsion. A
computation of the fermionant in polynomial time would solve
many interesting fermion sign problems.},
Key = {fds303643}
}

@article{fds245681,
Author = {Chandrasekharan, S and Li, A},
Title = {Fermion bag approach to the sign problem in strongly coupled
lattice QED with Wilson fermions},
Journal = {Journal of High Energy Physics},
Volume = {2011},
Number = {1},
Year = {2011},
ISSN = {1126-6708},
Abstract = {We explore the sign problem in strongly coupled lattice QED
with one flavor of Wilson fermions in four dimensions using
the fermion bag formulation. We construct rules to compute
the weight of a fermion bag and show that even though the
fermions are confined into bosons, fermion bags with
negative weights do exist. By classifying fermion bags as
either simple or complex, we find numerical evidence that
large complex bags with positive and negative weights come
with equal probabilities. On the other hand simple bags have
a large probability of having a positive weight. In analogy
with the meron cluster approach, we suggest that eliminating
the complex bags from the partition function should
alleviate the sign problem while capturing the important
physics. We also find a modified model containing only
simple bags which does not suffer from any sign problem and
argue that it contains a parity breaking phase transition
similar to the original model. We also prove that when the
hopping parameter is strictly infinite all fermion bags are
Doi = {10.1007/JHEP01(2011)018},
Key = {fds245681}
}

@article{fds245683,
Author = {Liu, DE and Chandrasekharan, S and Baranger, HU},
Title = {Quantum phase transition and emergent symmetry in a
Journal = {Physical Review Letters},
Volume = {105},
Number = {25},
Pages = {256801},
Year = {2010},
Month = {December},
url = {http://www.ncbi.nlm.nih.gov/pubmed/21231607},
Abstract = {We propose a system of four quantum dots designed to study
the competition between three types of interactions:
Heisenberg, Kondo, and Ising. We find a rich phase diagram
containing two sharp features: a quantum phase transition
(QPT) between charge-ordered and charge-liquid phases and a
dramatic resonance in the charge liquid visible in the
conductance. The QPT is of the Kosterlitz-Thouless type with
a discontinuous jump in the conductance at the transition.
We connect the resonance phenomenon with the degeneracy of
three levels in the isolated quadruple dot and argue that
this leads to a Kondo-like emergent symmetry from left-right
Z2 to U(1).},
Doi = {10.1103/PhysRevLett.105.256801},
Key = {fds245683}
}

@article{fds245682,
Author = {Chandrasekharan, S and Li, A},
Title = {Anomaly and a QCD-like phase diagram with massive bosonic
baryons},
Journal = {Journal of High Energy Physics},
Volume = {2010},
Number = {12},
Year = {2010},
ISSN = {1126-6708},
Abstract = {We study a strongly coupled Z 2 lattice gauge theory with
two flavors of quarks, invariant under an exact
SU(2)×SU(2)×U A(1)×U B(1) symmetry which is the same as
in QCD with two flavors of quarks without an anomaly. The
model also contains a coupling that can be used to break the
U A(1) symmetry and thus mimic the QCD anomaly. At low
temperatures T and small baryon chemical potential μ B the
model contains massless pions and massive bosonic baryons
similar to QCD with an even number of colors. In this work
we study the T - μ B phase diagram of the model and show
that it contains three phases: (1) A chirally broken phase
at low T and μ B, (2) a chirally symmetric baryon
superfluid phase at low T and high μ B, and (3) a symmetric
phase at high T. We find that the nature of the finite
temperature chiral phase transition and in particular the
location of the tricritical point that seperates the first
order line from the second order line is affected
significantly by the anomaly. © 2010 SISSA.},
Doi = {10.1007/JHEP12(2010)021},
Key = {fds245682}
}

@article{fds245684,
Author = {Liu, DE and Chandrasekharan, S and Baranger, HU},
Title = {Conductance of quantum impurity models from quantum monte
carlo},
Journal = {Physical Review B - Condensed Matter and Materials
Physics},
Volume = {82},
Number = {16},
Pages = {165447},
Year = {2010},
ISSN = {1098-0121},
url = {http://hdl.handle.net/10161/4258 Duke open
access},
Abstract = {The conductance of two Anderson impurity models, one with
twofold and another with fourfold degeneracy, representing
two types of quantum dots, is calculated using a world-line
quantum Monte Carlo (QMC) method. Extrapolation of the
imaginary time QMC data to zero frequency yields the linear
conductance, which is then compared to numerical
renormalization-group results in order to assess its
accuracy. We find that the method gives excellent results at
low temperature (T TK) throughout the mixed-valence and
Kondo regimes but it is unreliable for higher temperature.
© 2010 The American Physical Society.},
Doi = {10.1103/PhysRevB.82.165447},
Key = {fds245684}
}

@article{fds245685,
Author = {Chandrasekharan, S},
Title = {Fermion bag approach to lattice field theories},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {82},
Number = {2},
Pages = {025007},
Year = {2010},
ISSN = {1550-7998},
url = {http://hdl.handle.net/10161/4276 Duke open
access},
Abstract = {We propose a new approach to the fermion sign problem in
systems where there is a coupling U such that when it is
infinite the fermions are paired into bosons, and there is
no fermion permutation sign to worry about. We argue that as
U becomes finite, fermions are liberated but are naturally
confined to regions which we refer to as fermion bags. The
fermion sign problem is then confined to these bags and may
be solved using the determinantal trick. In the parameter
regime where the fermion bags are small and their typical
size does not grow with the system size, construction of
Monte Carlo methods that are far more efficient than
conventional algorithms should be possible. In the region
where the fermion bags grow with system size, the fermion
bag approach continues to provide an alternative approach to
the problem but may lose its main advantage in terms of
efficiency. The fermion bag approach also provides new
insights and solutions to sign problems. A natural solution
to the "silver blaze problem" also emerges. Using the
three-dimensional massless lattice Thirring model as an
example, we introduce the fermion bag approach and
demonstrate some of these features. We compute the critical
exponents at the quantum phase transition and find
ν=0.87(2) and η=0.62(2). © 2010 The American Physical
Society.},
Doi = {10.1103/PhysRevD.82.025007},
Key = {fds245685}
}

@article{fds245686,
Author = {Banerjee, D and Chandrasekharan, S},
Title = {Finite size effects in the presence of a chemical potential:
A study in the classical nonlinear O(2) sigma
model},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {81},
Number = {12},
Pages = {125007},
Year = {2010},
ISSN = {1550-7998},
url = {http://hdl.handle.net/10161/4275 Duke open
access},
Abstract = {In the presence of a chemical potential, the physics of
level crossings leads to singularities at zero temperature,
even when the spatial volume is finite. These singularities
are smoothed out at a finite temperature but leave behind
nontrivial finite size effects which must be understood in
order to extract thermodynamic quantities using Monte Carlo
methods, particularly close to critical points. We
illustrate some of these issues using the classical
nonlinear O(2) sigma model with a coupling β and chemical
potential μ on a 2+1-dimensional Euclidean lattice. In the
conventional formulation this model suffers from a sign
problem at nonzero chemical potential and hence cannot be
studied with the Wolff cluster algorithm. However, when
formulated in terms of the worldline of particles, the sign
problem is absent, and the model can be studied efficiently
with the "worm algorithm." Using this method we study the
finite size effects that arise due to the chemical potential
and develop an effective quantum mechanical approach to
capture the effects. As a side result we obtain energy
levels of up to four particles as a function of the box size
and uncover a part of the phase diagram in the (β,μ)
plane. © 2010 The American Physical Society.},
Doi = {10.1103/PhysRevD.81.125007},
Key = {fds245686}
}

@article{fds184647,
Author = {D. Podolski and S. Chandrasekharan and A.Vishwanath},
Title = {Phase Transitions of S=1 Spinor Condensates in an optical
lattice},
Journal = {Physical Review B},
Volume = {80},
Pages = {214513},
Year = {2009},
url = {http://prb.aps.org/abstract/PRB/v80/i21/e214513},
Abstract = {We study the phase diagram of spin-one polar condensates in
a two dimensional optical lattice with magnetic anisotropy.
We show that the topological binding of vorticity to nematic
disclinations allows for a rich variety of phase
transitions. These include Kosterlitz-Thouless-like
transitions with a superfluid stiffness jump that can be
experimentally tuned to take a continuous set of values, and
characterized by two divergent length scales. For higher
boson spin S, the thermal phase transitions are strongly
affected by the parity of S.},
Key = {fds184647}
}

@article{Podolsky:2007x,
Author = {Podolsky, D and Chandrasekharan, S and Vishwanath,
A},
Title = {Phase transitions of S=1 spinor condensates in an optical
lattice},
Journal = {Physical Review B - Condensed Matter and Materials
Physics},
Volume = {80},
Number = {21},
Year = {2009},
ISSN = {1098-0121},
url = {http://hdl.handle.net/10161/3298 Duke open
access},
Abstract = {We study the phase diagram of spin-one polar condensates in
a two-dimensional optical lattice with magnetic anisotropy.
We show that the topological binding of vorticity to nematic
disclinations allows for a rich variety of phase
transitions. These include Kosterlitz-Thouless-like
transitions with a superfluid stiffness jump that can be
experimentally tuned to take a continuous set of values, and
a cascaded Kosterlitz-Thouless transition, characterized by
two divergent length scales. For higher integer spin bosons
S, the thermal phase transition out of the planar polar
phase is strongly affected by the parity of S. © 2009 The
American Physical Society.},
Doi = {10.1103/PhysRevB.80.214513},
Key = {Podolsky:2007x}
}

@article{fds245704,
Author = {Kaul, RK and Ullmo, D and Zaránd, G and Chandrasekharan, S and Baranger, HU},
Title = {Ground state and excitations of quantum dots with magnetic
impurities},
Journal = {Physical Review B - Condensed Matter and Materials
Physics},
Volume = {80},
Number = {3},
Pages = {035318},
Year = {2009},
ISSN = {1098-0121},
Abstract = {We consider an "impurity" with a spin degree of freedom
coupled to a finite reservoir of noninteracting electrons, a
system which may be realized by either a true impurity in a
metallic nanoparticle or a small quantum dot coupled to a
large one. We show how the physics of such a spin impurity
is revealed in the many-body spectrum of the entire
finite-size system; in particular, the evolution of the
spectrum with the strength of the impurity-reservoir
coupling reflects the fundamental many-body correlations
present. Explicit calculation in the strong- and the
weak-coupling limits shows that the spectrum and its
evolution are sensitive to the nature of the impurity and
the parity of electrons in the reservoir. The effect of the
finite-size spectrum on two experimental observables is
considered. First, we propose an experimental setup in which
the spectrum may be conveniently measured using tunneling
spectroscopy. A rate equation calculation of the
differential conductance suggests how the many-body spectral
features may be observed. Second, the finite-temperature
magnetic susceptibility is presented, both the impurity and
the local susceptibilities. Extensive quantum Monte Carlo
calculations show that the local susceptibility deviates
from its bulk scaling form. Nevertheless, for special
assumptions about the reservoir-the "clean Kondo box"
model-we demonstrate that finite-size scaling is recovered.
Explicit numerical evaluations of these scaling functions
are given, both for even and odd parities and for the
canonical and the grand-canonical ensembles. © 2009 The
American Physical Society.},
Doi = {10.1103/PhysRevB.80.035318},
Key = {fds245704}
}

@article{Cecile:2008gs,
Author = {Cecile, DJ and Chandrasekharan, S},
Title = {Sigma-resonance and convergence of chiral perturbation
theory},
Journal = {PoS LATTICE},
Volume = {2008},
Pages = {071},
Year = {2008},
Month = {October},
url = {http://arxiv.org/abs/0810.2423v1},
Abstract = {The dimensionless parameter $\xi' = M^2/(16 \pi^2 F^2)$,
where $F$ is the pion decay constant in the chiral limit and
$M$ is the pion mass at leading order in the quark mass, is
expected to control the convergence of chiral perturbation
theory applicable to QCD. Here we demonstrate that a
strongly coupled lattice gauge theory model with the same
symmetries as two-flavor QCD but with a much lighter
$\sigma$-resonance is different. Our model allows us to
study efficiently the convergence of chiral perturbation
theory as a function of $\xi'$. We first confirm that the
leading low energy constants appearing in the chiral
Lagrangian are the same when calculated from the
$\epsilon$-regime and the $p$-regime. However, $\xi' \lesssim 0.002$ is necessary before 1-loop chiral
perturbation theory predicts the data within 1%. However,
for $\xi' > 0.0035$ the data begin to deviate qualitatively
from 1-loop chiral perturbation theory predictions. We argue
that this qualitative change is due to the presence of a
light $\sigma$-resonance in our model. Our findings may be
useful for lattice QCD studies.},
Key = {Cecile:2008gs}
}

@article{Chandrasekharan:2008gp,
Author = {Chandrasekharan, S},
Title = {A new computational approach to lattice quantum field
theories},
Journal = {PoS LATTICE},
Volume = {2008},
Pages = {003},
Year = {2008},
Month = {October},
url = {http://arxiv.org/abs/0810.2419v1},
Abstract = {Developments in algorithms over the past decade suggest that
there is a new computational approach to a class of quantum
field theories. This approach is based on rewriting the
partition function in a representation similar to the
world-line representation and hence we shall call it the
"WL-approach". This approach is likely to be more powerful
than the conventional approach in some regions of parameter
space, especially in the presence of chemical potentials or
massless fermions. While world-line representations are
natural in the Hamiltonian formulation, they can also be
constructed directly in Euclidean space. We first describe
the approach and its advantages by considering the classical
XY model in the presence of a chemical potential. We then
argue that, $CP^{N-1}$ models, models of pions on the
lattice and the lattice massless Thirring model, can all be
formulated and solved using the WL-approach. In particular,
we discover that the WL-approach to the Thirring model leads
to a novel determinantal Monte-Carlo algorithm which we call
the "dynamical-bag" algorithm. Finally, we argue that a
simple extension of the WL-approach to gauge theories leads
to a world-sheet, "WS-approach", in Abelian Lattice Gauge
theory.},
Key = {Chandrasekharan:2008gp}
}

@article{fds245669,
Author = {Jiang, F-J and Nyfeler, M and Chandrasekharan, S and Wiese,
U-J},
Title = {From an antiferromagnet to a valence bond solid: evidence
for a first-order phase transition},
Journal = {Journal of statistical mechanics (Online)},
Year = {2008},
Month = {February},
ISSN = {1742-5468},
Doi = {10.1088/1742-5468/2008/02/P02009},
Key = {fds245669}
}

@article{Cecile:2007dv,
Author = {Cecile, D. J. and Chandrasekharan, Shailesh},
Title = {Modeling pion physics in the $\epsilon$-regime of two-
flavor QCD using strong coupling lattice
QED},
Journal = {Phys. Rev.},
Volume = {D77},
Pages = {014506},
Year = {2008},
url = {http://arxiv.org/pdf/arXiv:0708.0558 [hep-lat]},
Abstract = {http://arxiv.org/abs/arXiv:0708.0558 [hep-lat]},
Key = {Cecile:2007dv}
}

@article{Chandrasekharan:2008gp,
Author = {Chandrasekharan, Shailesh},
Title = {A new computational approach to lattice quantum field
theories},
Journal = {PoS},
Volume = {LATTICE2008},
Pages = {003},
Year = {2008},
url = {http://arxiv.org/pdf/0810.2419},
Abstract = {http://arxiv.org/abs/0810.2419},
Key = {Chandrasekharan:2008gp}
}

@article{Chandrasekharan:2007sch,
Author = {Jiang, F.-J. and Nyfeler, M. and Chandrasekharan, S. and Wiese, U. -J.},
Title = {From an Antiferromagnet to a Valence Bond Solid: Evidence
for a First Order Phase Transition},
Journal = {J. of Stat. Mech},
Volume = {P02009},
Year = {2008},
Key = {Chandrasekharan:2007sch}
}

@article{chandrasekharan:077901,
Author = {S. Chandrasekharan and F.-J. Jiang and M. Pepe and U.-J.
Wiese},
Title = {Rotor spectra, berry phases, and monopole fields: From
antiferromagnets to QCD},
Journal = {Physical Review D (Particles and Fields)},
Volume = {78},
Number = {7},
Pages = {077901},
Publisher = {APS},
Year = {2008},
Key = {chandrasekharan:077901}
}

@article{Cecile:2008kp,
Author = {Cecile, D. J. and Chandrasekharan, Shailesh},
Title = {Role of the $\sigma$-resonance in determining the
convergence of chiral perturbation theory},
Journal = {Phys. Rev.},
Volume = {D77},
Pages = {091501},
Year = {2008},
url = {http://arxiv.org/pdf/0801.3823},
Abstract = {http://arxiv.org/abs/0801.3823},
Key = {Cecile:2008kp}
}

@article{Cecile:2008nb,
Author = {Cecile, D. J. and Chandrasekharan, Shailesh},
Title = {Absence of vortex condensation in a two dimensional
fermionic XY model},
Journal = {Phys. Rev.},
Volume = {D77},
Pages = {054502},
Year = {2008},
url = {http://arxiv.org/pdf/arXiv:0801.1857 [hep-lat]},
Abstract = {http://arxiv.org/abs/arXiv:0801.1857 [hep-lat]},
Key = {Cecile:2008nb}
}

@article{fds245705,
Author = {Cecile, DJ and Chandrasekharan, S},
Title = {Role of the σ resonance in determining the convergence of
chiral perturbation theory},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {77},
Number = {9},
Pages = {091501},
Year = {2008},
ISSN = {1550-7998},
Abstract = {The dimensionless parameter ξ=Mπ2/(16π2Fπ2), where Fπ
is the pion decay constant and Mπ is the pion mass, is
expected to control the convergence of chiral perturbation
theory applicable to QCD. Here we demonstrate that a
strongly coupled lattice gauge theory model with the same
symmetries as two-flavor QCD but with a much lighter
σ-resonance is different. We first confirm that the leading
low-energy constants appearing in the chiral Lagrangian are
the same when calculated from the p-regime and the -regime
as expected. However, ξ 0.002 is necessary before 1-loop
chiral perturbation theory predicts the data within 1%. For
ξ&gt;0.0035 the data begin to deviate dramatically from
1-loop chiral perturbation theory predictions. We argue that
this qualitative change is due to the presence of a light
σ-resonance in our model. Our findings may be useful for
lattice QCD studies. © 2008 The American Physical
Society.},
Doi = {10.1103/PhysRevD.77.091501},
Key = {fds245705}
}

@article{Chandrasekharan:2006wn,
Author = {Chandrasekharan, S and Jiang, F-J and Pepe, M and Wiese,
U-J},
Title = {Rotor spectra, berry phases, and monopole fields: From
antiferromagnets to QCD},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {78},
Number = {7},
Pages = {077901},
Year = {2008},
ISSN = {1550-7998},
url = {http://arxiv.org/pdf/cond-mat/0612252},
Abstract = {The order parameter of a finite system with a spontaneously
broken continuous global symmetry acts as a quantum
mechanical rotor. Both antiferromagnets with a spontaneously
broken SU(2)s spin symmetry and massless QCD with a broken
SU(2)L×SU(2)R chiral symmetry have rotor spectra when
considered in a finite volume. When an electron or hole is
doped into an antiferromagnet or when a nucleon is
propagating through the QCD vacuum, a Berry phase arises
from a monopole field and the angular momentum of the rotor
is quantized in half-integer units. © 2008 The American
Physical Society.},
Doi = {10.1103/PhysRevD.78.077901},
Key = {Chandrasekharan:2006wn}
}

@article{fds245707,
Author = {Jiang, F-J and Nyfeler, M and Chandrasekharan, S and Wiese,
U-J},
Title = {From an antiferromagnet to a valence bond solid: Evidence
for a first-order phase transition},
Journal = {Journal of statistical mechanics (Online)},
Volume = {2008},
Number = {2},
Pages = {P02009},
Year = {2008},
ISSN = {1742-5468},
url = {http://iopscience.iop.org/1742-5468/2008/02/P02009/},
Abstract = {Using a loop-cluster algorithm we investigate the spin-
Heisenberg antiferromagnet on a square lattice with exchange
coupling J and an additional four-spin interaction of
strength Q. We confirm the existence of a phase transition
separating antiferromagnetism at J/Q&gt;Jc/Q from a valence
bond solid (VBS) state at J/Q&lt;Jc/Q. Although our Monte
Carlo data are consistent with those of previous studies, we
do not confirm the existence of a deconfined quantum
critical point. Instead, using a flowgram method on lattices
as large as 802, we find evidence for a weak first-order
phase transition. We also present a detailed study of the
antiferromagnetic phase. For J/Q&gt;Jc/Q the staggered
magnetization, the spin stiffness and the spinwave velocity
of the antiferromagnet are determined by fitting Monte Carlo
data to analytic results from the systematic low-energy
effective field theory for magnons. Finally, we also
investigate the physics of the VBS state at J/Q&lt;Jc/Q and
we show that long but finite antiferromagnetic correlations
are still present. © 2008 IOP Publishing
Ltd.},
Doi = {10.1088/1742-5468/2008/02/P02009},
Key = {fds245707}
}

@article{fds245708,
Author = {Cecile, DJ and Chandrasekharan, S},
Title = {Absence of vortex condensation in a two dimensional
fermionic XY model},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {77},
Number = {5},
Pages = {054502},
Year = {2008},
ISSN = {1550-7998},
Abstract = {Motivated by a puzzle in the study of two-dimensional
lattice quantum electrodynamics with staggered fermions, we
construct a two-dimensional fermionic model with a global
U(1) symmetry. Our model can be mapped into a model of
closed packed dimers and plaquettes. Although the model has
the same symmetries as the XY model, we show numerically
that the model lacks the well-known Kosterlitz-Thouless
phase transition. The model is always in the gapless phase
showing the absence of a phase with vortex condensation. In
other words the low energy physics is described by a
noncompact U(1) field theory. We show that by introducing an
even number of layers one can introduce vortex condensation
within the model and thus also induce a Kosterlitz-Thouless
transition. © 2008 The American Physical
Society.},
Doi = {10.1103/PhysRevD.77.054502},
Key = {fds245708}
}

@article{fds245709,
Author = {Cecile, DJ and Chandrasekharan, S},
Title = {Modeling pion physics in the -regime of two-flavor QCD using
strong coupling lattice QED},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {77},
Number = {1},
Pages = {014506},
Year = {2008},
ISSN = {1550-7998},
Abstract = {In order to model pions of two-flavor QCD we consider a
lattice field theory involving two flavors of staggered
quarks interacting strongly with U(1) gauge fields. For
massless quarks, this theory has an SUL(2)×SUR(2) ×UA(1)
symmetry. By adding a four-fermion term we can break the
UA(1) symmetry and thus incorporate the physics of the QCD
anomaly. We can also tune the pion decay constant F, to be
small compared to the lattice cutoff by starting with an
extra fictitious dimension, thus allowing us to model low
energy pion physics in a setting similar to lattice QCD from
first principles. However, unlike lattice QCD, a major
advantage of our model is that we can easily design
efficient algorithms to compute a variety of quantities in
the chiral limit. Here we show that the model reproduces the
predictions of chiral perturbation theory in the -regime. ©
2008 The American Physical Society.},
Doi = {10.1103/PhysRevD.77.014506},
Key = {fds245709}
}

@article{fds245712,
Author = {Chandrasekharan, S and Mehta, AC},
Title = {Effects of the anomaly on the two-flavor QCD chiral phase
transition.},
Journal = {Physical Review Letters},
Volume = {99},
Number = {14},
Pages = {142004},
Year = {2007},
Month = {October},
ISSN = {0031-9007},
url = {http://www.ncbi.nlm.nih.gov/pubmed/17930663},
Abstract = {We use strongly coupled lattice QED with two flavors of
massless staggered fermions to model the chiral phase
transition in two-flavor massless QCD. Our model allows us
to vary the QCD anomaly and thus study its effects on the
transition. Our study confirms the widely accepted viewpoint
that the chiral phase transition is first order in the
absence of the anomaly. Turning on the anomaly weakens the
transition and turns it second order at a critical anomaly
strength. The anomaly strength at the tricritical point is
characterized using r=(M(eta')-M(pi))/rho(eta'), where
M(eta'), M(pi) are the screening masses of the anomalous and
regular pions and rho(eta') is the mass scale that governs
the low energy fluctuations of the anomalous symmetry. We
estimate that r ~ 7 in our model. This suggests that a
strong anomaly at the two-flavor QCD chiral phase transition
is necessary to wash out the first order
transition.},
Doi = {10.1103/PhysRevLett.99.142004},
Key = {fds245712}
}

@article{fds303652,
Author = {Chandrasekharan, S and Mehta, AC},
Title = {Effects of the anomaly on the two-flavor QCD chiral phase
transition},
Journal = {Phys.Rev.Lett.},
Volume = {99},
Pages = {142004},
Year = {2007},
Month = {May},
url = {http://arxiv.org/abs/0705.0617v1},
Abstract = {We use strongly coupled lattice QED with two flavors of
massless staggered fermions to model the physics of pions in
two-flavor massless QCD. Our model has the right chiral
symmetries and can be studied efficiently with cluster
algorithms. In particular we can tune the strength of the
QCD anomaly and thus study its effects on the chiral phase
transition. Our study confirms the widely accepted view
point that the chiral phase transition is first order in the
absence of the anomaly. Turning on the anomaly weakens the
transition and turns it second order at a critical anomaly
strength. The anomaly strength at the tricritical point is
characterized using $r = (M_{\eta'}-M_{\pi})/\rho_{\eta'}$
where $M_{\eta'}, M_{\pi}$ are the screening masses of the
anomalous and regular pions and $\rho_{\eta'}$ is the
mass-scale that governs the low energy fluctuations of the
anomalous symmetry. We estimate that $r \sim 7$ in our
model. This suggests that a strong anomaly at the two-flavor
QCD chiral phase transition is necessary to wash out the
first order transition.},
Doi = {10.1103/PhysRevLett.99.142004},
Key = {fds303652}
}

@article{Chandrasekharan:2007up,
Author = {Chandrasekharan, Shailesh and Mehta, Abhijit
C.},
Title = {Effects of the anomaly on the two-flavor QCD chiral phase
transition},
Journal = {Phys. Rev. Lett.},
Volume = {99},
Pages = {142004},
Year = {2007},
url = {http://arxiv.org/pdf/0705.0617},
Abstract = {http://arxiv.org/abs/0705.0617},
Key = {Chandrasekharan:2007up}
}

@article{fds245710,
Author = {Podolsky, D and Berkeley, UC and Chandrasekharan, S and Vishwanath,
A and Berkeley, UC and Berkeley, LBL},
Title = {Novel transitions in S=1 spinor condensates and XY
Ashkin-Teller universality},
Journal = {arXiv:0707.0695 [cond-mat.stat-mech]},
Year = {2007},
Abstract = {We study spin-1 polar spinor condensates with magnetic
anisotropy, in two spatial dimensions at finite
temperatures. The topological binding of vorticity to
nematic disclinations leads to a rich phase diagram, which
is captured by a U(1) version of the Ashkin-Teller model. In
particular, a "cascaded" Kosterlitz-Thouless critical point,
with two diverging scales, is predicted. Numerical
simulations are performed to check our picture.},
Key = {fds245710}
}

@article{fds245714,
Author = {Chandrasekharan, S},
Title = {Anomalous superfluidity in (2+1)-dimensional two-color
lattice QCD.},
Journal = {Physical Review Letters},
Volume = {97},
Number = {18},
Pages = {182001},
Year = {2006},
Month = {November},
ISSN = {0031-9007},
url = {http://www.ncbi.nlm.nih.gov/pubmed/17155536},
Abstract = {We study thermodynamics of strongly coupled lattice QCD with
two colors of staggered fermions in 2+1 dimensions. The
partition function of this model can be written elegantly as
a statistical mechanics of dimers and baryon loops. The
model is invariant under an SO(3) x U(1) symmetry. At low
temperatures, we find evidence for superfluidity in the U(1)
symmetry sector while the SO(3) symmetry remains unbroken.
The finite temperature phase transition appears to belong to
the Kosterlitz-Thouless universality class, but the
superfluid density jump rho(s) (T(c)) at the critical
temperature T(c) is anomalously higher than the normal value
of 2T(c)/pi. We show that, by adding a small SO(3) symmetry
breaking term to the model, the superfluid density jump
returns to its normal value, implying that the extra
symmetry causes anomalous superfluid behavior. Our results
may be of interest to researchers studying superfluidity in
spin-1 systems.},
Doi = {10.1103/PhysRevLett.97.182001},
Key = {fds245714}
}

@article{PhysRevLett.97.115703,
Author = {Priyadarshee, A and Chandrasekharan, S and Lee, J-W and Baranger,
HU},
Title = {Quantum phase transitions of hard-core bosons in background
potentials.},
Journal = {Physical Review Letters},
Volume = {97},
Number = {11},
Pages = {115703},
Year = {2006},
Month = {September},
ISSN = {0031-9007},
url = {http://www.ncbi.nlm.nih.gov/pubmed/17025902},
Abstract = {We study the zero temperature phase diagram of hard-core
bosons in two dimensions subjected to three types of
background potentials: staggered, uniform, and random. In
all three cases there is a quantum phase transition from a
superfluid (at small potential) to a normal phase (at large
potential), but with different universality classes. As
expected, the staggered case belongs to the XY universality,
while the uniform potential induces a mean field transition.
The disorder driven transition is clearly different from
both; in particular, we find z approximately 1.4, nu
approximately 1, and beta approximately 0.6.},
Doi = {10.1103/PhysRevLett.97.115703},
Key = {PhysRevLett.97.115703}
}

@article{fds245711,
Author = {Kaul, RK and Zaránd, G and Chandrasekharan, S and Ullmo, D and Baranger, HU},
Title = {Spectroscopy of the Kondo problem in a box.},
Journal = {Physical Review Letters},
Volume = {96},
Number = {17},
Pages = {176802},
Year = {2006},
Month = {May},
ISSN = {0031-9007},
url = {http://www.ncbi.nlm.nih.gov/pubmed/16712322},
Abstract = {Motivated by experiments on double quantum dots, we study
the problem of a single magnetic impurity confined in a
finite metallic host. We prove an exact theorem for the
ground state spin, and use analytic and numerical arguments
to map out the spin structure of the excitation spectrum of
the many-body Kondo-correlated state, throughout the weak to
strong coupling crossover. These excitations can be probed
in a simple tunneling-spectroscopy transport experiment; for
that situation we solve rate equations for the
conductance.},
Doi = {10.1103/PhysRevLett.96.176802},
Key = {fds245711}
}

@article{lee-2006,
Author = {Lee, Ji-Woo and Chandrasekharan, Shailesh and Baranger,
Harold U.},
Title = {Disorder-Induced Superfluidity in Hardcore Bosons in Two
Dimensions},
Year = {2006},
url = {http://arxiv.org/pdf/arXiv:0705.0617 [hep-lat]},
Abstract = {http://arxiv.org/abs/arXiv:0705.0617 [hep-lat]},
Key = {lee-2006}
}

@article{PhysRevLett.97.182001,
Author = {Chandrasekharan, Shailesh},
Title = {Anomalous Superfluidity in $(2+1)$-Dimensional Two-Color
Lattice QCD},
Journal = {Phys. Rev. Lett.},
Volume = {97},
Number = {18},
Pages = {182001},
Year = {2006},
Key = {PhysRevLett.97.182001}
}

@article{PhysRevLett.96.176802,
Author = {Kaul, Ribhu K. and Zar\'and, Gergely and Chandrasekharan,
Shailesh and Ullmo, Denis and Baranger, Harold
U.},
Title = {Spectroscopy of the Kondo Problem in a Box},
Journal = {Phys. Rev. Lett.},
Volume = {96},
Number = {17},
Pages = {176802},
Year = {2006},
Key = {PhysRevLett.96.176802}
}

@article{Chandrasekharan:2006tz,
Author = {Chandrasekharan, Shailesh and Jiang, Fu-Jiun},
Title = {Phase-diagram of two-color lattice QCD in the chiral
limit},
Journal = {Phys. Rev.},
Volume = {D74},
Pages = {014506},
Year = {2006},
url = {http://arxiv.org/pdf/hep-lat/0602031},
Abstract = {http://arxiv.org/abs/hep-lat/0602031},
Key = {Chandrasekharan:2006tz}
}

@article{Chandrasekharan:2006iw,
Author = {Chandrasekharan, S},
Title = {New approaches to strong coupling lattice
QCD},
Journal = {Int. J. Mod. Phys.},
Volume = {B20},
Pages = {2714-2723},
Year = {2006},
Key = {Chandrasekharan:2006iw}
}

@article{fds245713,
Author = {Chandrasekharan, S and Jiang, F-J},
Title = {Phase diagram of two-color lattice QCD in the chiral
limit},
Journal = {Physical Review D - Particles, Fields, Gravitation, and
Cosmology},
Volume = {74},
Number = {1},
Pages = {014506},
Year = {2006},
ISSN = {1550-7998},
Abstract = {We study thermodynamics of strongly coupled lattice QCD with
two colors of massless staggered fermions as a function of
the baryon chemical potential μ in 3+1 dimensions using a
new cluster algorithm. We find evidence that the model
undergoes a weak first order phase transition at μ=0 which
becomes second order at a finite μ. Symmetry considerations
suggest that the universality class of these phase
transitions should be governed by a O(N)×O(2) field theory
with collinear order, with N=3 at μ=0 and N=2 at μ≠0.
The universality class of the second order phase transition
at μ≠0 appears to be governed by the decoupled XY fixed
point present in the O(2)×O(2) field theory. Finally we
show that the quantum (T=0) phase transition as a function
of μ is a second order mean field transition. © 2006 The
American Physical Society.},
Doi = {10.1103/PhysRevD.74.014506},
Key = {fds245713}
}

@article{Chandrasekharan:2005dn,
Author = {Chandrasekharan, S and Jiang, F-J},
Title = {Chiral limit of 2-color QCD at strong couplings},
Journal = {PoS LAT},
Volume = {2005},
Pages = {198},
Year = {2005},
Month = {September},
url = {http://arxiv.org/abs/hep-lat/0509117v1},
Abstract = {We study two-color lattice QCD with massless staggered
fermions in the strong coupling limit using a new and
efficient cluster algorithm. We focus on the phase diagram
of the model as a function of temperature $T$ and baryon
chemical potential $\mu$ by working on $L_t \times L^d$
lattices in both $d=2,3$. In $d=3$ we find that at $\mu=0$
the ground state of the system breaks the global U(2)
symmetry present in the model to U(1), while the finite
temperature phase transition (with $L_t=4$) which restores
the symmetry is a weak first order transition. In $d=2$ we
find evidence for a novel phase transition similar to the
Berezinky-Kosterlitz-Thouless phenomena. On the other hand
the quantum (T=0) phase transition to a symmetric phase as a
function of $\mu$ is second order in both $d=2,3$ and
belongs to the mean field universality class.},
Key = {Chandrasekharan:2005dn}
}

@article{Yoo:2004mh,
Author = {Yoo, J and Chandrasekharan, S and Baranger, HU},
Title = {Multilevel algorithm for quantum-impurity
models.},
Journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter
Physics},
Volume = {71},
Number = {3 Pt 2B},
Pages = {036708},
Year = {2005},
Month = {March},
ISSN = {1539-3755},
url = {http://www.ncbi.nlm.nih.gov/pubmed/15903634},
Abstract = {A continuous-time path integral quantum Monte Carlo method
using the directed-loop algorithm is developed to simulate
the Anderson single-impurity model in the occupation number
basis. Although the method suffers from a sign problem at
low temperatures, the new algorithm has many advantages over
conventional algorithms. For example, the model can be
easily simulated in the Kondo limit without time
discretization errors. Furthermore, many observables
including the impurity susceptibility and a variety of
fermionic observables can be calculated efficiently. Finally
the new approach allows us to explore a general technique,
called the multilevel algorithm, to solve the sign problem.
We find that the multilevel algorithm is able to generate an
exponentially large number of configurations with an effort
that grows as a polynomial in inverse temperature such that
configurations with a positive sign dominate over those with
negative signs. Our algorithm can be easily generalized to
other multi-impurity problems.},
Doi = {10.1103/PhysRevE.71.036708},
Key = {Yoo:2004mh}
}

@article{fds245715,
Author = {Chandrasekharan, S and Strouthos, CG},
Title = {Failure of mean field theory at large N.},
Journal = {Physical Review Letters},
Volume = {94},
Number = {6},
Pages = {061601},
Year = {2005},
Month = {February},
ISSN = {0031-9007},
url = {http://www.ncbi.nlm.nih.gov/pubmed/15783719},
Abstract = {We study strongly coupled lattice QCD with N colors of
staggered fermions in 3+1 dimensions. While mean field
theory describes the low temperature behavior of this theory
at large N, it fails in the scaling region close to the
finite temperature second order chiral phase transition. The
universal critical region close to the phase transition
belongs to the 3D XY universality class even when N becomes
large. This is in contrast to Gross-Neveu models where the
critical region shrinks as N (the number of flavors)
increases and mean field theory is expected to describe the
phase transition exactly in the limit of infinite N. Our
work demonstrates that infrared fluctuations can be
important close to second order phase transitions even when
N is strictly infinite.},
Doi = {10.1103/PhysRevLett.94.061601},
Key = {fds245715}
}

@article{Chandrasekharan:2004uw,
Author = {Chandrasekharan, Shailesh and Strouthos, Costas
G.},
Title = {Failure of mean field theory at large N},
Journal = {Phys. Rev. Lett.},
Volume = {94},
Pages = {061601},
Year = {2005},
url = {http://arxiv.org/pdf/hep-lat/0410036},
Abstract = {http://arxiv.org/abs/hep-lat/0410036},
Key = {Chandrasekharan:2004uw}
}

@article{PhysRevB.72.024525,
Author = {Lee, J-W and Chandrasekharan, S and Baranger, HU},
Title = {Quantum Monte Carlo study of disordered fermions},
Journal = {Physical Review B - Condensed Matter and Materials
Physics},
Volume = {72},
Number = {2},
Pages = {024525},
Year = {2005},
ISSN = {1098-0121},
url = {http://dx.doi.org/10.1103/PhysRevB.72.024525},
Abstract = {We study a strongly correlated fermionic model with
attractive interactions in the presence of disorder in two
spatial dimensions. Our model has been designed so that it
can be solved using the recently discovered meron-cluster
approach. Although the model is unconventional it has the
same symmetries as the Hubbard model. Since the naive
algorithm is inefficient, we develop an algorithm by
combining the meron-cluster technique with the directed-loop
update. This combination allows us to compute the pair
susceptibility and the winding number susceptibility
accurately. We find that the s -wave superconductivity,
present in the clean model, does not disappear until the
disorder reaches a temperature dependent critical strength.
The critical behavior as a function of disorder close to the
phase transition belongs to the Berezinky-Kosterlitz-Thouless
universality class as expected. The fermionic degrees of
freedom, although present, do not appear to play an
important role near the phase transition. © 2005 The
American Physical Society.},
Doi = {10.1103/PhysRevB.72.024525},
Key = {PhysRevB.72.024525}
}

@article{Kaul04_mesokondo,
Author = {Kaul, RK and Ullmo, D and Chandrasekharan, S and Baranger,
HU},
Title = {Mesoscopic Kondo problem},
Journal = {Europhysics Letters},
Volume = {71},
Number = {6},
Pages = {973-979},
Year = {2005},
url = {http://www.phy.duke.edu/research/cmtheory/bg/paper/kaulucb04_mesokondo.pdf},
Abstract = {We study the effect of mesoscopic fluctuations on a magnetic
impurity coupled to a spatially confined electron gas with a
temperature in the mesoscopic range (i.e. between the mean
level spacing Δ and the Thouless energy ETh). Comparing
"poor-man's scaling" with exact Quantum Monte Carlo, we find
that for temperatures larger than the Kondo temperature,
many aspects of the fluctuations can be captured by the
perturbative technique. Using this technique in conjunction
with semi-classical approximations, we are able to calculate
the mesoscopic fluctuations for a wide variety of systems.
For temperatures smaller than the Kondo temperature, we find
large fluctuations and deviations from the universal
Doi = {10.1209/epl/i2005-10184-1},
Key = {Kaul04_mesokondo}
}

@article{PhysRevB.71.201309,
Author = {Yoo, J and Chandrasekharan, S and Kaul, RK and Ullmo, D and Baranger,
HU},
Title = {Cluster algorithms for quantum impurity models and
mesoscopic Kondo physics},
Journal = {Physical Review B - Condensed Matter and Materials
Physics},
Volume = {71},
Number = {20},
Pages = {201309},
Year = {2005},
url = {http://dx.doi.org/10.1103/PhysRevB.71.201309},
Abstract = {Nanoscale physics and dynamical mean-field theory have both
generated increased interest in complex quantum impurity
problems and so have focused attention on the need for
flexible quantum impurity solvers. Here we demonstrate that
the mapping of single-quantum impurity problems onto spin
chains can be exploited to yield a powerful and extremely
flexible impurity solver. We implement this cluster
algorithm explicitly for the Anderson and Kondo
Hamiltonians, and illustrate its use in the "mesoscopic
Kondo problem." To study universal Kondo physics, a large
ratio between the effective bandwidth Deff and the
temperature T is required; our cluster algorithm treats the
mesoscopic fluctuations exactly while being able to approach
the large Deff T limit with ease. We emphasize that the
flexibility of our method allows it to tackle a wide variety
of quantum impurity problems; thus, it may also be relevant
to the dynamical mean-field theory of lattice problems. ©
2005 The American Physical Society.},
Doi = {10.1103/PhysRevB.71.201309},
Key = {PhysRevB.71.201309}
}

@article{Yoo05_HFsign,
Author = {Yoo, J and Chandrasekharan, S and Kaul, RK and Ullmo, D and Baranger,
HU},
Title = {On the sign problem in the Hirsch-Fye algorithm for impurity
problems},
Journal = {Journal of Physics A: Mathematical and General},
Volume = {38},
Number = {48},
Pages = {10307-10310},
Year = {2005},
url = {http://www.phy.duke.edu/research/cmtheory/bg/paper/yooCKUB05_hfsign.pdf},
Abstract = {We show that there is no fermion sign problem in the Hirsch
and Fye algorithm for the single-impurity Anderson model.
Beyond the particle-hole symmetric case for which a simple
proof exists, this has been known only empirically. Here we
prove the nonexistence of a sign problem for the general
case by showing that each spin trace for a given Ising
configuration is separately positive. We further use this
insight to analyse under what conditions orbitally
degenerate Anderson models or the two-impurity Anderson
model develop a sign. © 2005 IOP Publishing
Ltd.},
Doi = {10.1088/0305-4470/38/48/004},
Key = {Yoo05_HFsign}
}

@article{Chandrasekharan:2004kd,
Author = {Chandrasekharan, Shailesh and Strouthos, Costas
G.},
Title = {Connecting lattice QCD with chiral perturbation theory at
strong coupling},
Journal = {Phys. Rev. D},
Volume = {69},
Pages = {091502},
Year = {2004},
url = {http://arxiv.org/pdf/hep-lat/0401002},
Abstract = {http://arxiv.org/abs/hep-lat/0401002},
Key = {Chandrasekharan:2004kd}
}

@article{Brower:2003vy,
Author = {Brower, R. and Chandrasekharan, S. and Riederer, S. and Wiese, U. J.},
Title = {D-theory: Field quantization by dimensional reduction of
discrete variables},
Journal = {Nucl. Phys. B},
Volume = {693},
Pages = {149-175},
Year = {2004},
url = {http://arxiv.org/pdf/hep-lat/0309182},
Abstract = {http://arxiv.org/abs/hep-lat/0309182},
Key = {Brower:2003vy}
}

@article{Chandrasekharan:2004cn,
Author = {Chandrasekharan, S and Wiese, U-J},
Title = {An introduction to chiral symmetry on the
lattice},
Journal = {Progress in Particle and Nuclear Physics},
Volume = {53},
Number = {2},
Pages = {373-418},
Year = {2004},
url = {http://arxiv.org/pdf/hep-lat/0405024},
Abstract = {The SU(Nf)L⊗SU(Nf)R chiral symmetry of QCD is of central
importance for the nonperturbative low-energy dynamics of
light quarks and gluons. Lattice field theory provides a
theoretical framework in which these dynamics can be studied
from first principles. The implementation of chiral symmetry
on the lattice is a nontrivial issue. In particular, local
lattice fermion actions with the chiral symmetry of the
continuum theory suffer from the fermion doubling problem.
The Ginsparg-Wilson relation implies Lüscher's lattice
variant of chiral symmetry which agrees with the usual one
in the continuum limit. Local lattice fermion actions that
obey the Ginsparg-Wilson relation have an exact chiral
symmetry, the correct axial anomaly, they obey a lattice
version of the Atiyah-Singer index theorem, and still they
do not suffer from the notorious doubling problem. The
Ginsparg-Wilson relation is satisfied exactly by Neuberger's
overlap fermions which are a limit of Kaplan's domain wall
fermions, as well as by Hasenfratz and Niedermayer's
classically perfect lattice fermion actions. When chiral
symmetry is nonlinearly realized in effective field theories
on the lattice, the doubling problem again does not arise.
This review provides an introduction to chiral symmetry on
the lattice with an emphasis on the basic theoretical
B.V.},
Doi = {10.1016/j.ppnp.2004.05.003},
Key = {Chandrasekharan:2004cn}
}

@article{Chandrasekharan:2003ug,
Author = {Chandrasekharan, S},
Title = {Chiral and critical in strong coupling QCD},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {129-130},
Pages = {578-580},
Year = {2004},
url = {http://arxiv.org/pdf/hep-lat/0309098},
Abstract = {We use a cluster algorithm to study the critical behavior of
strongly coupled lattice QCD in the chiral limit. We show
that the finite temperature chiral phase transition belongs
to the O(2) universality class as expected. When we compute
the finite size effects of the chiral susceptibility in the
low temperature phase close to the transition, we find clear
evidence for chiral singularities predicted by chiral
perturbation theory (ChPT). On the other hand it is
difficult to reconcile the quark mass dependence of various
quantities near the chiral limit with ChPT. © 2004
Doi = {10.1016/S0920-5632(03)02647-1},
Key = {Chandrasekharan:2003ug}
}

@article{Chandrasekharan:2003ub,
Author = {Chandrasekharan, S and Pepe, M and Steffen, FD and Wiese,
U-J},
Title = {Lattice theories with nonlinearly realized chiral
symmetry},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {129-130},
Pages = {507-509},
Year = {2004},
url = {http://arxiv.org/pdf/hep-lat/0309093},
Abstract = {We present the lattice formulation of effective Lagrangians
in which chiral symmetry is realized nonlinearly on the
fermion fields. In this framework both the Wilson term
removing unphysical doubler fermions and the fermion mass
term do not break chiral symmetry. Our lattice formulation
allows us to address non-perturbative questions in effective
theories of baryons interacting with pions and in models
involving constitutent quarks interacting with pions and
gluons. With the presented methods, a system containing a
non-zero density of static baryons interacting with pions
can be studied on the lattice without encountering a complex
action problem. This might lead to new insights into the
phase diagram of strongly interacting matter at non-zero
chemical potential. © 2004 Elsevier B.V. All rights
reserved.},
Doi = {10.1016/S0920-5632(03)02624-0},
Key = {Chandrasekharan:2003ub}
}

@article{fds245717,
Author = {Brower, R and Chandrasekharan, S and Riederer, S and Wiese,
U-J},
Title = {D-theory: Field quantization by dimensional reduction of
discrete variables},
Journal = {Nuclear Physics B},
Volume = {693},
Number = {1-3},
Pages = {149-175},
Year = {2004},
url = {http://dx.doi.org/10.1016/j.nuclphysb.2004.06.007},
Abstract = {D-theory is an alternative non-perturbative approach to
quantum field theory formulated in terms of discrete
quantized variables instead of classical fields. Classical
scalar fields are replaced by generalized quantum spins and
classical gauge fields are replaced by quantum links. The
classical fields of a d-dimensional quantum field theory
reappear as low-energy effective degrees of freedom of the
discrete variables, provided the (d+1)-dimensional D-theory
is massless. When the extent of the extra Euclidean
dimension becomes small in units of the correlation length,
an ordinary d-dimensional quantum field theory emerges by
dimensional reduction. The D-theory formulation of scalar
field theories with various global symmetries and of gauge
theories with various gauge groups is constructed explicitly
and the mechanism of dimensional reduction is investigated.
Doi = {10.1016/j.nuclphysb.2004.06.007},
Key = {fds245717}
}

@article{fds245720,
Author = {Chandrasekharan, S and Strouthos, CG},
Title = {Connecting lattice QCD with chiral perturbation theory at
strong coupling},
Journal = {Physical Review D: Particles, Fields, Gravitation and
Cosmology},
Volume = {69},
Number = {9},
Pages = {091502},
Year = {2004},
ISSN = {0556-2821},
url = {http://dx.doi.org/10.1103/PhysRevD.69.091502},
Abstract = {We study the difficulties associated with detecting chiral
singularities predicted by chiral perturbation theory (ChPT)
in lattice QCD. We focus on the physics of the remnant O(2)
chiral symmetry of staggered fermions in the strong coupling
limit using the recently discovered directed path algorithm.
Since it is easier to look for powerlike singularities as
compared to logarithmic ones, our calculations are performed
at a fixed finite temperature in the chirally broken phase.
We show that the behavior of the chiral condensate, the pion
mass, and the pion decay constant are all consistent with
the predictions of ChPT for small masses. However, in order
to demonstrate this we need quark masses that are much
smaller (in lattice units) than those typically used in
dynamical QCD simulations. We also need to use higher order
terms in the chiral expansion to fit our data. © 2004 The
American Physical Society.},
Doi = {10.1103/PhysRevD.69.091502},
Key = {fds245720}
}

@article{fds303653,
Author = {Chandrasekharan, S and Pepe, M and Steffen, FD and Wiese,
U-J},
Title = {Nonlinear Realization of Chiral Symmetry on the
Lattice},
Journal = {JHEP},
Volume = {0312},
Pages = {035},
Year = {2003},
Month = {June},
url = {http://arxiv.org/abs/hep-lat/0306020v2},
Abstract = {We formulate lattice theories in which chiral symmetry is
realized nonlinearly on the fermion fields. In this
framework the fermion mass term does not break chiral
symmetry. This property allows us to use the Wilson term to
remove the doubler fermions while maintaining exact chiral
symmetry on the lattice. Our lattice formulation enables us
to address non-perturbative questions in effective field
theories of baryons interacting with pions and in models
involving constituent quarks interacting with pions and
gluons. We show that a system containing a non-zero density
of static baryons interacting with pions can be studied on
the lattice without encountering complex action problems. In
our formulation one can also decide non-perturbatively if
the chiral quark model of Georgi and Manohar provides an
appropriate low-energy description of QCD. If so, one could
understand why the non-relativistic quark model
works.},
Doi = {10.1088/1126-6708/2003/12/035},
Key = {fds303653}
}

@article{Chandrasekharan:2002vk,
Author = {Chandrasekharan, S. and Cox, J. and Osborn, J. C. and Wiese,
U. J.},
Title = {Meron-Cluster Approach to Systems of Strongly Correlated
Electrons},
Journal = {Nucl. Phys. B},
Volume = {673},
Pages = {405-436},
Year = {2003},
url = {http://arxiv.org/pdf/cond-mat/0201360},
Abstract = {http://arxiv.org/abs/cond-mat/0201360},
Key = {Chandrasekharan:2002vk}
}

@article{Chandrasekharan:2003im,
Author = {Chandrasekharan, Shailesh and Jiang, Fu-Jiun},
Title = {Chiral limit of strongly coupled lattice QCD at finite
temperatures},
Journal = {Phys. Rev. D},
Volume = {68},
Pages = {091501},
Year = {2003},
url = {http://arxiv.org/pdf/hep-lat/0309025},
Abstract = {http://arxiv.org/abs/hep-lat/0309025},
Key = {Chandrasekharan:2003im}
}

@article{Chandrasekharan:2003eu,
Author = {Chandrasekharan, S.},
Title = {Connections between quantum chromodynamics and condensed
matter physics},
Journal = {Pramana},
Volume = {61},
Pages = {901-910},
Year = {2003},
Key = {Chandrasekharan:2003eu}
}

Author = {Adams, David H. and Chandrasekharan, Shailesh},
Title = {Chiral limit of strongly coupled lattice gauge
theories},
Journal = {Nucl. Phys. B},
Volume = {662},
Pages = {220-246},
Year = {2003},
url = {http://arxiv.org/pdf/hep-lat/0303003},
Abstract = {http://arxiv.org/abs/hep-lat/0303003},
}

@article{Chandrasekharan:2003wy,
Author = {Chandrasekharan, S. and Pepe, M. and Steffen, F. D. and Wiese, U. J.},
Title = {Nonlinear realization of chiral symmetry on the
lattice},
Journal = {JHEP},
Volume = {12},
Pages = {035},
Year = {2003},
url = {http://arxiv.org/pdf/hep-lat/0306020},
Abstract = {http://arxiv.org/abs/hep-lat/0306020},
Key = {Chandrasekharan:2003wy}
}

@article{Chandrasekharan:2003qv,
Author = {Chandrasekharan, Shailesh and Strouthos, Costas
G.},
Title = {Kosterlitz-Thouless universality in dimer
models},
Journal = {Phys. Rev. D},
Volume = {68},
Pages = {091502},
Year = {2003},
url = {http://arxiv.org/pdf/hep-lat/0306034},
Abstract = {http://arxiv.org/abs/hep-lat/0306034},
Key = {Chandrasekharan:2003qv}
}

@article{fds29982,
Author = {S. Chandrasekharan},
Title = {CHIRAL LIMIT OF STAGGERED FERMIONS AT STRONG COUPLINGS: A
LOOP REPRESENTATION},
Journal = {Nucl. Phys. B (Proceedings Suppl.)},
Volume = {119},
Pages = {929},
Editor = {Edwards, Negele and Richards},
Year = {2003},
Abstract = {The partition function of two dimensional massless staggered
fermions interacting with U(N) gauge fields is rewritten in
terms of loop variables in the strong coupling limit. We use
this representation of the theory to devise a non-local
Metropolis algorithm to calculate the chiral susceptibility.
For small lattices our algorithm reproduces exact results
quite accurately. Applying this algorithm to large volumes
yields rather surprising results. In particular we find
$m_\pi \neq 0$ for all $N$ and it increases with $N$. Since
the talk was presented we have found reasons to believe that
our algorithm breaks down for large volumes questioning the
validity of our results.},
Key = {fds29982}
}

@article{fds245676,
Author = {Chandrasekharan, S and Pepe, M and Steffen, FD and Wiese,
U-J},
Title = {Nonlinear realization of chiral symmetry on the
lattice},
Journal = {The Journal of High Energy Physics},
Volume = {7},
Number = {12},
Pages = {831-863},
Year = {2003},
ISSN = {1029-8479},
Abstract = {We formulate lattice theories in which chiral symmetry is
realized nonlinearly on the fermion fields. In this
framework the fermion mass term does not break chiral
symmetry. This property allows us to use the Wilson term to
remove the doubler fermions while maintaining exact chiral
symmetry on the lattice. Our lattice formulation enables us
to address non-perturbative questions in effective field
theories of baryons interacting with pions and in models
involving constituent quarks interacting with pions and
gluons. We show that a system containing a non-zero density
of static baryons interacting with pions can be studied on
the lattice without encountering complex action problems. In
our formulation one can also decide non-perturbatively if
the chiral quark model of Georgi and Manohar provides an
appropriate low-energy description of QCD. If so, one could
understand why the non-relativistic quark model works. ©
SISSA/ISAS 2004.},
Key = {fds245676}
}

@article{Brower:2003yx,
Author = {Brower, R and Chandrasekharan, S and Negele, JW and Wiese,
U-J},
Title = {QCD at fixed topology},
Journal = {Physics Letters, Section B: Nuclear, Elementary Particle and
High-Energy Physics},
Volume = {560},
Number = {1-2},
Pages = {64-74},
Year = {2003},
url = {http://arxiv.org/pdf/hep-lat/0302005},
Abstract = {Since present Monte Carlo algorithms for lattice QCD may
become trapped in a fixed topological charge sector, it is
important to understand the effect of calculating at fixed
topology. In this Letter, we show that although the
restriction to a fixed topological sector becomes irrelevant
in the infinite volume limit, it gives rise to
characteristic finite-size effects due to contributions from
all θ-vacua. We calculate these effects and show how to
extract physical results from numerical data obtained at
B.V.},
Doi = {10.1016/S0370-2693(03)00369-1},
Key = {Brower:2003yx}
}

@article{Chandrasekharan:2002gp,
Author = {Chandrasekharan, S},
Title = {Chiral limit of staggered fermions at strong couplings: A
loop representation},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {119},
Pages = {929-931},
Year = {2003},
url = {http://arxiv.org/pdf/hep-lat/0208071},
Abstract = {The partition function of two dimensional massless staggered
fermions interacting with U(N) gauge fields is rewritten in
terms of loop variables in the strong coupling limit. We use
this representation of the theory to devise a non-local
Metropolis algorithm to calculate the chiral susceptibility.
For small lattices our algorithm reproduces exact results
quite accurately. Applying this algorithm to large volumes
yields rather surprising results. In particular we find mπ
≠ 0 for all N and it increases with N. Since the talk was
presented we have found reasons to believe that our
algorithm breaks down for large volumes questioning the
validity of our results.},
Doi = {10.1016/S0920-5632(03)01722-5},
Key = {Chandrasekharan:2002gp}
}

@article{fds245716,
Author = {Chandrasekharan, S},
Title = {Connections between quantum chromodynamics and condensed
matter physics},
Journal = {Pramana - Journal of Physics},
Volume = {61},
Number = {5},
Pages = {901-910},
Year = {2003},
Abstract = {Features of QCD can be seen qualitatively in certain
condensed matter systems. Recently some of the analyses that
originated in condensed matter physics have found
applications in QCD. Using examples we discuss some of the
connections between the two fields and show how progress can
be made by exploiting this connection. Some of the
challenges that remain in the two fields are quite similar.
We argue that recent algorithmic developments call for
optimism in both fields.},
Key = {fds245716}
}

@article{fds245718,
Author = {Chandrasekharan, S and Strouthos, CG},
Title = {Kosterlitz-Thouless universality in dimer
models},
Journal = {Physical Review D: Particles, Fields, Gravitation and
Cosmology},
Volume = {68},
Number = {9},
Pages = {091502},
Year = {2003},
ISSN = {0556-2821},
url = {http://dx.doi.org/10.1103/PhysRevD.68.091502},
Abstract = {Using the monomer-dimer representation of strongly coupled
U(N) lattice gauge theories with staggered fermions, we
study finite temperature chiral phase transitions in 2+1
dimensions. A new cluster algorithm allows us to compute
monomer-monomer and dimer-dimer correlations at zero monomer
density (chiral limit) accurately on large lattices. This
makes it possible to show convincingly, for the first time,
that these models undergo a finite temperature phase
transition which belongs to the Kosterlitz-Thouless
universality class. We find that the phase transition
persists for all values of N, but occurs at different values
of the critical temperature Tc. Further, when T /Tc is held
fixed, the mean field analysis often used in the large N
limit breaks down. © The American Physical
Society.},
Doi = {10.1103/PhysRevD.68.091502},
Key = {fds245718}
}

@article{fds245719,
Author = {Chandrasekharan, S and Jiang, F-J},
Title = {Chiral limit of strongly coupled lattice QCD at finite
temperatures},
Journal = {Physical Review D: Particles, Fields, Gravitation and
Cosmology},
Volume = {68},
Number = {9},
Pages = {091501},
Year = {2003},
ISSN = {0556-2821},
url = {http://dx.doi.org/10.1103/PhysRevD.68.091501},
Abstract = {We use the recently proposed directed-path algorithm to
study the chiral limit of a strongly coupled lattice QCD
with staggered quarks at finite temperatures. The new
algorithm allows us to compute the chiral susceptibility and
the pion decay constant accurately on large lattices for
massless quarks. In the low temperature phase we find clear
evidence for the singularities predicted by chiral
perturbation theory. We also show convincingly that the
chiral phase transition is of second order and belongs to
the O(2) universality class. © The American Physical
Society.},
Doi = {10.1103/PhysRevD.68.091501},
Key = {fds245719}
}

@article{fds245721,
Author = {Chandrasekharan, S and Cox, J and Osborn, JC and Wiese,
U-J},
Title = {Meron-cluster approach to systems of strongly correlated
electrons},
Journal = {Nuclear Physics B},
Volume = {673},
Number = {3},
Pages = {405-436},
Year = {2003},
url = {http://dx.doi.org/10.1016/j.nuclphysb.2003.08.041},
Abstract = {Numerical simulations of strongly correlated electron
systems suffer from the notorious fermion sign problem which
has prevented progress in understanding if systems like the
Hubbard model display high-temperature superconductivity.
Here we show how the fermion sign problem can be solved
completely with meron-cluster methods in a large class of
models of strongly correlated electron systems, some of
which are in the extended Hubbard model family and show
s-wave superconductivity. In these models we also find that
on-site repulsion can even coexist with a weak chemical
potential without introducing sign problems. We argue that
since these models can be simulated efficiently using
cluster algorithms they are ideal for studying many of the
interesting phenomena in strongly correlated electron
systems. © 2003 Elsevier B.V. All rights
reserved.},
Doi = {10.1016/j.nuclphysb.2003.08.041},
Key = {fds245721}
}

@article{fds245722,
Author = {Adams, DH and Chandrasekharan, S},
Title = {Chiral limit of strongly coupled lattice gauge
theories},
Journal = {Nuclear Physics B},
Volume = {662},
Number = {1-2},
Pages = {220-246},
Year = {2003},
url = {http://dx.doi.org/10.1016/S0550-3213(03)00350-X},
Abstract = {We construct a new and efficient cluster algorithm for
updating strongly coupled U(N) lattice gauge theories with
staggered fermions in the chiral limit. The algorithm uses
the constrained monomer-dimer representation of the theory
and should also be of interest to researchers working on
other models with similar constraints. Using the new
algorithm we address questions related to the chiral limit
of strongly coupled U(N) gauge theories beyond the mean
field approximation. We show that the infinite volume chiral
condensate is non-zero in three and four dimensions.
However, on a square lattice of size L we find
∑x〈ψ̄ψ(x)ψ̄ψ(0)〉∼ L2-η for large L where
η=0.420(3)/N+0.078(4) /N2. These results differ from an
earlier conclusion obtained using a different algorithm.
Here we argue that the earlier calculations were misleading
due to uncontrolled autocorrelation times encountered by the
previous algorithm. © 2003 Elsevier Science B.V. All rights
reserved.},
Doi = {10.1016/S0550-3213(03)00350-X},
Key = {fds245722}
}

@article{fds245723,
Author = {Brower, R and Chandrasekharan, S and Negele, JW and Wiese,
U-J},
Title = {LATTICE QCD AT FIXED TOPOLOGY},
Journal = {Phys. Lett. B},
Volume = {560},
Pages = {64-74},
Year = {2003},
Abstract = {Since present Monte Carlo algorithms for lattice QCD may
become trapped in a fixed topological charge sector, it is
important to understand the effect of calculating at fixed
topology. In this work, we show that although the
restriction to a fixed topological sector becomes irrelevant
in the infinite volume limit, it gives rise to
characteristic finite size effects due to contributions from
all $\theta$-vacua. We calculate these effects and show how
to extract physical results from numerical data obtained at
fixed topology.},
Key = {fds245723}
}

@article{Brower:2001cz,
Author = {Brower, R. and Chandrasekharan, S. and Negele, J. W. and Wiese, U. J.},
Title = {Physical observables from lattice QCD at fixed
topology},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {106},
Pages = {581-583},
Year = {2002},
url = {http://arxiv.org/pdf/hep-lat/0110121},
Abstract = {http://arxiv.org/abs/hep-lat/0110121},
Key = {Brower:2001cz}
}

@article{Chandrasekharan:2001ya,
Author = {Chandrasekharan, S. and Scarlet, B. and Wiese, U.
J.},
Title = {From spin ladders to the 2-d O(3) model at non-zero
density},
Journal = {Comput. Phys. Commun.},
Volume = {147},
Pages = {388-393},
Year = {2002},
url = {http://arxiv.org/pdf/hep-lat/0110215},
Abstract = {http://arxiv.org/abs/hep-lat/0110215},
Key = {Chandrasekharan:2001ya}
}

@article{Chandrasekharan:2002ex,
Author = {Chandrasekharan, Shailesh},
Title = {Unexpected results in the chiral limit with staggered
fermions},
Journal = {Phys. Lett. B},
Volume = {536},
Pages = {72-78},
Year = {2002},
url = {http://arxiv.org/pdf/hep-lat/0203020},
Abstract = {http://arxiv.org/abs/hep-lat/0203020},
Key = {Chandrasekharan:2002ex}
}

@article{PhysRevB.66.045113,
Author = {Chandrasekharan, S and Osborn, JC},
Title = {Kosterlitz-Thouless universality in a fermionic
system},
Journal = {Physical Review B - Condensed Matter and Materials
Physics},
Volume = {66},
Number = {4},
Pages = {451131-451135},
Year = {2002},
ISSN = {0163-1829},
Abstract = {An extension of the attractive Hubbard model is constructed
to study the critical behavior near a finite-temperature
superconducting phase transition in two dimensions using the
recently developed meron-cluster algorithm. Unlike previous
calculations in the attractive Hubbard model which were
limited to small lattices, the algorithm is used to study
the critical behavior on lattices as large as 128 × 128.
These precise results show that a fermionic system can
undergo a finite temperature phase transition whose critical
behavior is well described by the predictions of Kosterlitz
and Thouless almost three decades ago. In particular it is
confirmed that the spatial winding number susceptibility
obeys the well known predictions of finite size scaling for
T &lt;Tc and up to logarithmic corrections the pair
susceptibility scales as L2-η at large volumes with 0 ≤
η ≤ 0.25 for 0 ≤T≤T.},
Key = {PhysRevB.66.045113}
}

@article{Chandrasekharan:2001dd,
Author = {Chandrasekharan, S},
Title = {Superconductivity and chiral symmetry breaking with fermion
clusters},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {106-107},
Pages = {1025-1027},
Year = {2002},
url = {http://arxiv.org/pdf/hep-lat/0110125},
Abstract = {Cluster variables have recently revolutionized numerical
work in certain models involving fermionic variables. This
novel representation of fermionic partition functions is
continuing to find new applications. After describing
results from a study of a two dimensional Hubbard type model
that confirm a superconducting transition in the
Kosterlitz-Thouless universality class, we show how a
cluster type algorithm can be devised to study the chiral
limit of strongly coupled lattice gauge theories with
staggered fermions.},
Doi = {10.1016/S0920-5632(01)01917-X},
Key = {Chandrasekharan:2001dd}
}

@article{fds245746,
Author = {Brower, R and Chandrasekharan, S and Negele, JW and Wiese,
U-J},
Title = {Physical observables from lattice QCD at fixed
topology},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {106-107},
Pages = {581-583},
Year = {2002},
url = {http://dx.doi.org/10.1016/S0920-5632(01)01784-4},
Abstract = {Because present Monte Carlo algorithms for lattice QCD may
become trapped in a given topological charge sector when one
approaches the continuum limit, it is important to
understand the effect of calculating at fixed topology. In
this work, we show that although the restriction to a fixed
topological sector becomes irrelevant in the infinite volume
limit, it gives rise to characteristic finite size effects
due to contributions from all θ-vacua. We calculate these
effects and show how to extract physical results from
numerical data obtained at fixed topology.},
Doi = {10.1016/S0920-5632(01)01784-4},
Key = {fds245746}
}

@article{fds245747,
Author = {Chandrasekharan, S and Scarlet, B and Wiese, U-J},
Title = {From spin ladders to the 2D O(3) model at non-zero
density},
Journal = {Computer Physics Communications},
Volume = {147},
Number = {1-2},
Pages = {388-393},
Year = {2002},
url = {http://dx.doi.org/10.1016/S0010-4655(02)00311-9},
Abstract = {The numerical simulation of various field theories at
non-zero chemical potential suffers from severe complex
action problems. In particular, QCD at non-zero quark
density can presently not be simulated for that reason. A
similar complex action problem arises in the 2D O(3) model -
a toy model for QCD. Here we construct the 2D O(3) model at
non-zero density via dimensional reduction of an
antiferromagnetic quantum spin ladder in a magnetic field.
The complex action problem of the 2D O(3) model manifests
itself as a sign problem of the ladder system. This sign
problem is solved completely with a meron cluster algorithm.
© 2002 Elsevier Science B.V. All rights
reserved.},
Doi = {10.1016/S0010-4655(02)00311-9},
Key = {fds245747}
}

@article{fds245748,
Author = {Chandrasekharan, S},
Title = {Unexpected results in the chiral limit with staggered
fermions},
Journal = {Physics Letters B},
Volume = {536},
Number = {1-2},
Pages = {72-78},
Year = {2002},
ISSN = {0370-2693},
url = {http://dx.doi.org/10.1016/S0370-2693(02)01816-6},
Abstract = {A cluster algorithm is constructed and applied to study the
chiral limit of the strongly coupled lattice Schwinger model
involving staggered fermions. The algorithm is based on a
novel loop representation of the model. Finite size scaling
of the chiral susceptibility based on data from lattices of
size up to 64 × 64 indicates the absence of long range
correlations at strong couplings. Assuming that there is no
phase transition at a weaker coupling, the results imply
that all mesons acquire a mass at non-zero lattice spacings.
Although this does not violate any known physics, it is
surprising since typically one expects a single pion to
remain massless at non-zero lattice spacings in the
staggered fermion formulation. © 2002 Elsevier Science B.V.
Doi = {10.1016/S0370-2693(02)01816-6},
Key = {fds245748}
}

@article{fds303645,
Author = {Chandrasekharan, S},
Title = {Novel Quantum Monte Carlo Algorithms for
Fermions},
Year = {2001},
Month = {October},
url = {http://arxiv.org/abs/hep-lat/0110018v1},
Abstract = {Recent research shows that the partition function for a
class of models involving fermions can be written as a
statistical mechanics of clusters with positive definite
weights. This new representation of the model allows one to
construct novel algorithms. We illustrate this through
models consisting of fermions with and without spin. A
Hubbard type model with both attractive and repulsive
interactions becomes tractable using the new approach.
Precision results in the two dimensional attractive model
confirm a superfluid phase transition in the
Kosterlitz-Thouless universality class.},
Key = {fds303645}
}

@article{fds303656,
Author = {Chandrasekharan, S and Osborn, JC},
Title = {Kosterlitz-Thouless Universality in a Fermionic
System},
Volume = {66},
Pages = {045113},
Year = {2001},
Month = {September},
url = {http://arxiv.org/abs/cond-mat/0109424v1},
Abstract = {A new extension of the attractive Hubbard model is
constructed to study the critical behavior near a finite
temperature superconducting phase transition in two
dimensions using the recently developed meron-cluster
algorithm. Unlike previous calculations in the attractive
Hubbard model which were limited to small lattices, the new
algorithm is used to study the critical behavior on lattices
as large as $128\times 128$. These precise results for the
first time show that a fermionic system can undergo a finite
temperature phase transition whose critical behavior is well
described by the predictions of Kosterlitz and Thouless
almost three decades ago. In particular it is confirmed that
the spatial winding number susceptibility obeys the well
known predictions of finite size scaling for $T<T_c$ and up
to logarithmic corrections the pair susceptibility scales as
$L^{2-\eta}$ at large volumes with $0\leq\eta\leq 0.25$ for
$0\leq T\leq T_c$.},
Doi = {10.1103/PhysRevB.66.045113},
Key = {fds303656}
}

@article{Alford:2001ug,
Author = {Alford, Mark G. and Chandrasekharan, S. and Cox, J. and Wiese, U. J.},
Title = {Solution of the complex action problem in the Potts model
for dense QCD},
Journal = {Nucl. Phys. B},
Volume = {602},
Pages = {61-86},
Year = {2001},
url = {http://arxiv.org/pdf/hep-lat/0101012},
Abstract = {http://arxiv.org/abs/hep-lat/0101012},
Key = {Alford:2001ug}
}

@article{Chandrasekharan:2001cj,
Author = {Chandrasekharan, Shailesh},
Title = {Novel quantum Monte Carlo algorithms for
fermions},
Year = {2001},
url = {http://arxiv.org/pdf/hep-lat/0110018},
Abstract = {http://arxiv.org/abs/hep-lat/0110018},
Key = {Chandrasekharan:2001cj}
}

@article{Chandrasekharan:2000fd,
Author = {Chandrasekharan, S. and Chudnovsky, V. and Schlittgen, B. and Wiese, U. J.},
Title = {Flop transitions in cuprate and color superconductors: From
SO(5) to SO(10) unification?},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {94},
Pages = {449-452},
Year = {2001},
url = {http://arxiv.org/pdf/hep-lat/0011054},
Abstract = {http://arxiv.org/abs/hep-lat/0011054},
Key = {Chandrasekharan:2000fd}
}

@article{Chandrasekharan:2000ew,
Author = {Chandrasekharan, Shailesh},
Title = {QCD at a finite density of static quarks},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {94},
Pages = {71-78},
Year = {2001},
url = {http://arxiv.org/pdf/hep-lat/0011022},
Abstract = {http://arxiv.org/abs/hep-lat/0011022},
Key = {Chandrasekharan:2000ew}
}

@article{Chandrasekharan:2000fr,
Author = {Chandrasekharan, S and Osborn, J},
Title = {Solving sign problems with meron algorithms},
Journal = {Springer Proceedings in Physics},
Volume = {86},
Pages = {28-42},
Year = {2001},
ISSN = {0930-8989},
Key = {Chandrasekharan:2000fr}
}

@article{fds245743,
Author = {Chandrasekharan, S},
Title = {QCD at a finite density of static quarks},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {94},
Number = {1-3},
Pages = {71-78},
Year = {2001},
url = {http://dx.doi.org/10.1016/S0920-5632(01)00936-7},
Abstract = {Recently, cluster methods have been used to solve a variety
of sign problems including those that arise in the presence
of fermions. In all cases an analytic partial re-summation
over a class of configurations in the path integral was
necessary. Here the new ideas are illustrated using the
example of QCD at a finite density of static quarks. In this
limit the sign problem simplifies since the fermionic part
decouples. Furthermore, the problem can be solved completely
when the gauge dynamics is replaced by a Potts model. On the
other hand in QCD with light quarks the solution will
require a partial re-summation over both fermionic and gauge
degrees of freedom. The new approach points to unexplored
directions in the search for a solution to this more
challenging sign problem. © 2001 Elsevier Science B.V. All
rights reserved.},
Doi = {10.1016/S0920-5632(01)00936-7},
Key = {fds245743}
}

@article{fds245744,
Author = {Alford, M and Chandrasekharan, S and Cox, J and Wiese,
U-J},
Title = {Solution of the complex action problem in the Potts model
for dense QCD},
Journal = {Nuclear Physics B},
Volume = {602},
Number = {1-2},
Pages = {61-86},
Year = {2001},
url = {http://dx.doi.org/10.1016/S0550-3213(01)00068-2},
Abstract = {Monte Carlo simulations of lattice QCD at non-zero baryon
chemical potential μ suffer from the notorious complex
action problem. We consider QCD with static quarks coupled
to a large chemical potential. This leaves us with an SU(3)
Yang-Mills theory with a complex action containing the
Polyakov loop. Close to the deconfinement phase transition
the qualitative features of this theory, in particular its
Z(3) symmetry properties, are captured by the 3-d 3-state
Potts model. We solve the complex action problem in the
Potts model by using a cluster algorithm. The improved
estimator for the μ-dependent part of the Boltzmann factor
is real and positive and is used for importance sampling. We
localize the critical endpoint of the first order
deconfinement phase transition line and find consistency
with universal 3-d Ising behavior. We also calculate the
static quark-quark, quark-antiquark, and antiquark-antiquark
potentials which show screening as expected for a system
with non-zero baryon density.},
Doi = {10.1016/S0550-3213(01)00068-2},
Key = {fds245744}
}

@article{fds245745,
Author = {Chandrasekharan, S and Chudnovsky, V and Schlittgen, B and Wiese,
U-J},
Title = {Flop transitions in cuprate and color superconductors: From
SO(5) to SO(10) unification?},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {94},
Number = {1-3},
Pages = {449-452},
Year = {2001},
url = {http://dx.doi.org/10.1016/S0920-5632(01)01002-7},
Abstract = {The phase diagrams of cuprate superconductors and of QCD at
non-zero baryon chemical potential are qualitatively
similar. The Néel phase of the cuprates corresponds to the
chirally broken phase of QCD, and the high-temperature
superconducting phase corresponds to the color
superconducting phase. In the SO(5) theory for the cuprates
the SO(3)s spin rotational symmetry and the U(1)em gauge
symmetry of electromagnetism are dynamically unified. This
suggests that the SU(2)L ⊗ SU(2)R ⊗ U(1)B chiral
symmetry of QCD and the SU(3)c color gauge symmetry may get
unified to SO(10). Dynamical enhancement of symmetry from
SO(2)s ⊗ Z(2) to SO(3)s is known to occur in anisotropic
antiferromagnets. In these systems the staggered
magnetization flops from an easy 3-axis into the 12-plane at
a critical value of the external magnetic field. Similarly,
the phase transitions in the SO(5) and SO(10) models are
flop transitions of a "superspin". Despite this fact, a
renormalization group flow analysis in 4 - ε dimensions
indicates that a point with full SO(5) or SO(10) symmetry
exists neither in the cuprates nor in QCD. © 2001 Elsevier
Doi = {10.1016/S0920-5632(01)01002-7},
Key = {fds245745}
}

@article{fds303644,
Author = {Chandrasekharan, S and Wiese, U-J},
Title = {SO(10) Unification of Color Superconductivity and Chiral
Symmetry Breaking?},
Year = {2000},
Month = {March},
url = {http://arxiv.org/abs/hep-ph/0003214v1},
Abstract = {Motivated by the SO(5) theory of high-temperature
superconductivity and antiferromagnetism, we ask if an
SO(10) theory unifies color superconductivity and chiral
symmetry breaking in QCD. The transition to the color
superconducting phase would then be analogous to a spin flop
transition. While the spin flop transition generically has a
unified SO(3) description, the SO(5) and SO(10) symmetric
fixed points are unstable, at least in (4 - epsilon)
dimensions, and require the fine-tuning of one additional
relevant parameter. If QCD is near the SO(10) fixed point,
it has interesting consequences for heavy ion collisions and
neutron stars.},
Key = {fds303644}
}

@article{Chandrasekharan:2000dj,
Author = {Chandrasekharan, S},
Title = {A Chiral Phase Transition using a Fermion Cluster
Algorithm},
Journal = {Chin.J.Phys.},
Volume = {38},
Pages = {696-706},
Year = {2000},
Month = {January},
url = {http://arxiv.org/abs/hep-lat/0001003v1},
Abstract = {The recent solution to the fermion sign problem allows, for
the first time, the use of cluster algorithm techniques to
compute certain fermionic path integrals. To illustrate the
underlying ideas behind the progress, a cluster algorithm is
constructed to study the chiral phase transition in a
strongly interacting staggered fermion model with an
arbitrary mass term in 3+1 dimensions. Unlike conventional
methods there is no difficulty in the cluster method to
approach the chiral (massless) limit. Results using the new
algorithm confirm that the chiral transition falls under the
expected universality class.},
Key = {Chandrasekharan:2000dj}
}

@article{Chandrasekharan:1999ys,
Author = {Chandrasekharan, S. and Cox, J. and Holland, K. and Wiese,
U. J.},
Title = {Meron-cluster simulation of a chiral phase transition with
staggered fermions},
Journal = {Nucl. Phys. B},
Volume = {576},
Pages = {481-500},
Year = {2000},
url = {http://arxiv.org/pdf/hep-lat/9906021},
Abstract = {http://arxiv.org/abs/hep-lat/9906021},
Key = {Chandrasekharan:1999ys}
}

@article{Chandrasekharan:2000gk,
Author = {Chandrasekharan, Shailesh and Wiese, Uwe-Jens},
Title = {SO(10) unification of color superconductivity and chiral
symmetry breaking?},
Year = {2000},
url = {http://arxiv.org/pdf/hep-ph/0003214},
Abstract = {http://arxiv.org/abs/hep-ph/0003214},
Key = {Chandrasekharan:2000gk}
}

@article{Chandrasekharan:2000rm,
Author = {Chandrasekharan, Shailesh and Osborn, James
C.},
Title = {Critical behavior of a chiral condensate with a meron
cluster algorithm},
Journal = {Phys. Lett. B},
Volume = {496},
Pages = {122-128},
Year = {2000},
url = {http://arxiv.org/pdf/hep-lat/0010036},
Abstract = {http://arxiv.org/abs/hep-lat/0010036},
Key = {Chandrasekharan:2000rm}
}

@article{Chandrasekharan:1999vz,
Author = {Chandrasekharan, S},
Title = {Fermion cluster algorithms},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {83-84},
Number = {1-3},
Pages = {774-776},
Year = {2000},
url = {http://arxiv.org/pdf/hep-lat/9909007},
Abstract = {Cluster algorithms have been recently used to eliminate sign
problems that plague Monte-Carlo methods in a variety of
systems. In particular such algorithms can also be used to
solve sign problems associated with the permutation of
fermion world lines. This solution leads to the possibility
of designing fermion cluster algorithms in certain cases.
Using the example of free non-relativistic fermions we
discuss the ideas underlying the algorithm.},
Key = {Chandrasekharan:1999vz}
}

@article{fds245740,
Author = {Chandrasekharan, S and Cox, J and Holland, K and Wiese,
U-J},
Title = {Meron-cluster simulation of a chiral phase transition with
staggered fermions},
Journal = {Nuclear Physics B},
Volume = {576},
Number = {1-3},
Pages = {481-500},
Year = {2000},
Abstract = {We examine a (3 + 1)-dimensional model of staggered lattice
fermions with a four-fermion interaction and ℤ(2) chiral
symmetry using the Hamiltonian formulation. This model
cannot be simulated with standard fermion algorithms because
those suffer from a very severe sign problem. We use a new
fermion simulation technique - the meron-cluster algorithm -
which solves the sign problem and leads to high-precision
numerical data. We investigate the finite temperature chiral
phase transition and verify that it is in the universality
class of the 3-d Ising model using finite-size scaling. ©
Key = {fds245740}
}

@article{fds245742,
Author = {Chandrasekharan, S and Osborn, JC},
Title = {Critical behavior of a chiral condensate with a meron
cluster algorithm},
Journal = {Physics Letters B},
Volume = {496},
Number = {1-2},
Pages = {122-128},
Year = {2000},
ISSN = {0370-2693},
url = {http://dx.doi.org/10.1016/S0370-2693(00)01294-6},
Abstract = {A new meron cluster algorithm is constructed to study the
finite temperature critical behavior of the chiral
condensate in a (3 + 1)-dimensional model of interacting
staggered fermions. Using finite size scaling analysis the
infinite volume condensate is shown to be consistent with
the behavior of the form (Tc - T)0.314(7) for temperatures
less than the critical temperature and m1/4.87(10) at the
critical temperature confirming that the critical behavior
belongs to the 3-d Ising universality class within one to
two sigma deviation. The new method, along with improvements
in the implementation of the algorithm, allows the
determination of the critical temperature Tc more accurately
than was possible in a previous study. © 2000 Elsevier
Science B.V.},
Doi = {10.1016/S0370-2693(00)01294-6},
Key = {fds245742}
}

@article{fds303642,
Author = {Chandrasekharan, S and Scarlet, B and Wiese, U-J},
Title = {Meron-Cluster Simulation of Quantum Spin Ladders in a
Magnetic Field},
Year = {1999},
Month = {September},
url = {http://arxiv.org/abs/cond-mat/9909451v1},
Abstract = {Numerical simulations of numerous quantum systems suffer
from the notorious sign problem. Meron-cluster algorithms
lead to an efficient solution of sign problems for both
fermionic and bosonic models. Here we apply the meron
concept to quantum spin systems in an arbitrary external
magnetic field, in which case standard cluster algorithms
fail. As an example, we simulate antiferromagnetic quantum
spin ladders in a uniform external magnetic field that
competes with the spin-spin interaction. The numerical
results are in agreement with analytic predictions for the
magnetization as a function of the external
field.},
Key = {fds303642}
}

@article{Chandrasekharan:1998wg,
Author = {Chandrasekharan, Shailesh},
Title = {Lattice QCD with Ginsparg-Wilson fermions},
Journal = {Phys. Rev. D},
Volume = {60},
Pages = {074503},
Year = {1999},
url = {http://arxiv.org/pdf/hep-lat/9805015},
Abstract = {http://arxiv.org/abs/hep-lat/9805015},
Key = {Chandrasekharan:1998wg}
}

@article{Chandrasekharan:1999zt,
Author = {Chandrasekharan, S. and Scarlet, B. and Wiese, U.
J.},
Title = {Meron-Cluster Simulation of Quantum Spin Ladders in a
Magnetic Field},
Year = {1999},
url = {http://arxiv.org/pdf/cond-mat/9909451},
Abstract = {http://arxiv.org/abs/cond-mat/9909451},
Key = {Chandrasekharan:1999zt}
}

@article{Chandrasekharan:1999cm,
Author = {Chandrasekharan, Shailesh and Wiese, Uwe-Jens},
Title = {Meron-cluster solution of a fermion sign
problem},
Journal = {Phys. Rev. Lett.},
Volume = {83},
Pages = {3116-3119},
Year = {1999},
url = {http://arxiv.org/pdf/cond-mat/9902128},
Abstract = {http://arxiv.org/abs/cond-mat/9902128},
Key = {Chandrasekharan:1999cm}
}

@article{Chandrasekharan:1998yx,
Author = {Chandrasekharan, Shailesh and others},
Title = {Anomalous chiral symmetry breaking above the QCD phase
transition},
Journal = {Phys. Rev. Lett.},
Volume = {82},
Pages = {2463-2466},
Year = {1999},
url = {http://arxiv.org/pdf/hep-lat/9807018},
Abstract = {http://arxiv.org/abs/hep-lat/9807018},
Key = {Chandrasekharan:1998yx}
}

@article{Bhattacharya:1999uq,
Author = {Bhattacharya, Tanmoy and Chandrasekharan, Shailesh and Gupta, Rajan and Lee, Weon-Jong and Sharpe, Stephen
R.},
Title = {Non-perturbative renormalization constants using Ward
identities},
Journal = {Phys. Lett. B},
Volume = {461},
Pages = {79-88},
Year = {1999},
url = {http://arxiv.org/pdf/hep-lat/9904011},
Abstract = {http://arxiv.org/abs/hep-lat/9904011},
Key = {Bhattacharya:1999uq}
}

@article{Chandrasekharan:1998ck,
Author = {Chandrasekharan, Shailesh},
Title = {Confinement, chiral symmetry breaking and continuum limits
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {73},
Pages = {739-741},
Year = {1999},
url = {http://arxiv.org/pdf/hep-lat/9809084},
Abstract = {http://arxiv.org/abs/hep-lat/9809084},
Key = {Chandrasekharan:1998ck}
}

@article{Chandrasekharan:1998em,
Author = {Chandrasekharan, S},
Title = {Ginsparg-Wilson fermions: A study in the Schwinger
model},
Journal = {Physical Review D - Particles, Fields, Gravitation and
Cosmology},
Volume = {59},
Number = {9},
Pages = {1-8},
Year = {1999},
url = {http://arxiv.org/pdf/hep-lat/9810007},
Abstract = {The qualitative features of Ginsparg-Wilson fermions, as
formulated by Neuberger, coupled to two-dimensional U(1)
gauge theory are studied. The role of the Wilson mass
parameter in changing the number of massless flavors in the
theory and its connection with the index of the Dirac
operator is studied. Although the index of the Dirac
operator is not related to the geometric definition of the
topological charge for strong couplings, the two start to
agree as soon as one goes to moderately weak couplings. This
produces the desired singularity in the quenched chiral
condensate which appears to be very difficult to reproduce
with staggered fermions. The fermion determinant removes the
singularity and reproduces the known chiral condensate and
the meson mass within understandable errors. ©1999 The
American Physical Society.},
Key = {Chandrasekharan:1998em}
}

@article{fds245673,
Author = {Chandrasekharan, S},
Title = {Lattice QCD with Ginsparg-Wilson fermions},
Journal = {Physical Review D - Particles, Fields, Gravitation and
Cosmology},
Volume = {60},
Number = {7},
Pages = {1-6},
Year = {1999},
url = {http://arxiv.org/abs/hep-lat/9805015v3},
Abstract = {Lattice QCD using fermions whose Dirac operator obeys the
Ginsparg-Wilson relation is perhaps the best known
formulation of QCD with a finite cutoff. It reproduces all
the low energy QCD phenomenology associated with chiral
symmetry at finite lattice spacings. In particular it
explains the origin of massless pions due to spontaneous
chiral symmetry breaking and leads to new ways to approach
the U(1) problem on the lattice. Here we show these results
in the path integral formulation and derive for the first
time in lattice QCD a known formal continuum relation
between the chiral condensate and the topological
susceptibility. This relation leads to predictions for the
critical behavior of the topological susceptibility near the
phase transition and can now be checked in Monte Carlo
simulations even at finite lattice spacings. ©1999 The
American Physical Society.},
Doi = {10.1103/PhysRevD.60.074503},
Key = {fds245673}
}

@article{Brower:1997ha,
Author = {Brower, R and Chandrasekharan, S and Wiese, U-J},
Title = {QCD as a quantum link model},
Journal = {Physical Review D: Particles, Fields, Gravitation and
Cosmology},
Volume = {60},
Number = {9},
Pages = {DUMMY42},
Year = {1999},
ISSN = {0556-2821},
url = {http://arxiv.org/pdf/hep-th/9704106},
Abstract = {QCD is constructed as a lattice gauge theory in which the
elements of the link matrices are represented by
non-commuting operators acting in a Hubert space. The
resulting quantum link model for QCD is formulated with a
fifth Euclidean dimension, whose extent resembles the
inverse gauge coupling of the resulting fourdimensional
theory after dimensional reduction. The inclusion of quarks
is natural in Shamir's variant of Kaplan's fermion method,
which does not require fine-tuning to approach the chiral
limit. A rishon representation in terms of fermionic
constituents of the gluons is derived and the quantum link
Hamiltonian for QCD with a U(N) gauge symmetry is expressed
in terms of glueball, meson and constituent quark operators.
The new formulation of QCD is promising both from an
analytic and from a computational point of view. ©1999 The
American Physical Society.},
Key = {Brower:1997ha}
}

@article{Bhattacharya:1998ue,
Author = {Bhattacharya, T and Chandrasekharan, S and Gupta, R and Lee, W and Sharpe, S},
Title = {Non-perturbative renormalization constants using Ward
identities},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {73},
Number = {1-3},
Pages = {276-278},
Year = {1999},
url = {http://arxiv.org/pdf/hep-lat/9810018},
Abstract = {We extend the application of vector and axial Ward
identities to calculate bA, bP and bT, coefficients that
give the mass dependence of the renormalization constants of
the corresponding bilinear operators in the quenched theory.
The extension relies on using operators with non-degenerate
quark masses. It allows a complete determination of the O(a)
improvement coefficients for bilinears in the quenched
approximation using Ward Identities alone. Only the scale
dependent normalization constants Z0P (or Z0S) and ZT are
undetermined. We present results of a pilot numerical study
Key = {Bhattacharya:1998ue}
}

@article{fds245736,
Author = {Bhattacharya, T and Chandrasekharan, S and Gupta, R and Lee, W and Sharpe, S},
Title = {Non-perturbative renormalization constants using Ward
identities 1},
Journal = {Physics Letters, Section B: Nuclear, Elementary Particle and
High-Energy Physics},
Volume = {461},
Number = {1-2},
Pages = {79-88},
Year = {1999},
Abstract = {We extend the application of axial Ward identities to
calculate bA, bp and bT, coefficients that give the mass
dependence of the renormalization constants of the
corresponding bilinear operators in the quenched theory. The
extension relies on using operators with non-degenerate
quark masses. It allows a complete determination of the O(a)
improvement coefficients for bilinears in the quenched
approximation using Ward Identities alone. Only the scale
dependent normalization constants ZP0 (or ZS0) and ZT are
undetermined. We present results of a pilot numerical study
Key = {fds245736}
}

@article{fds245738,
Author = {Chandrasekharan, S},
Title = {Confinement, chiral symmetry breaking and continuum limits
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {73},
Number = {1-3},
Pages = {739-741},
Year = {1999},
Abstract = {Using the example of compact U(1) lattice gauge theory we
argue that quantum link models can be used to reproduce the
physics of conventional Hamiltonian lattice gauge theories.
In addition to the usual gauge coupling g, these models have
a new parameter j which naturally cuts-off large electric
flux quanta on each link while preserving exact U(1) gauge
invariance. The j → ∞ limit recovers the conventional
Hamiltonian. At strong couplings, the theory shows
confinement and chiral symmetry breaking for all non-trivial
values of j. The phase diagram of the 3+1 dimensional theory
suggests that a coulomb phase is present at large but finite
j. Setting g = 0, a new approach to the physics of compact
U(1) gauge theory on the lattice emerges. In this case the
parameter j takes over the role of the gauge coupling, and j
→ ∞ describes free photons.},
Key = {fds245738}
}

@article{fds245739,
Author = {Chandrasekharan, S and Chen, D and Christ, N and Lee, W and Mawhinney,
R and Vranas, P},
Title = {Anomalous chiral symmetry breaking above the QCD phase
transition},
Journal = {Physical Review Letters},
Volume = {82},
Number = {12},
Pages = {2463-2466},
Year = {1999},
Abstract = {We study the anomalous breaking of UA(1) symmetry just above
the QCD phase transition for zero and two flavors of quarks,
using a staggered fermion, lattice discretization. The
properties of the QCD phase transition are expected to
depend on the degree of UA(1) symmetry breaking in the
transition region. For the physical case of two flavors, we
carry out extensive simulations on a 163 × 4 lattice,
measuring a difference in susceptibilities which is
sensitive to UA(1) symmetry and which avoids many of the
staggered fermion discretization difficulties. The results
suggest that anomalous effects are at or below the 15%
level. © 1999 The American Physical Society.},
Key = {fds245739}
}

@article{fds245741,
Author = {Chandrasekharan, S and Wiese, U-J},
Title = {Meron-Cluster Solution of Fermion Sign Problems},
Journal = {Physical Review Letters},
Volume = {83},
Number = {16},
Pages = {3116-3119},
Year = {1999},
Abstract = {We present a general strategy to solve the notorious fermion
sign problem using cluster algorithms. The method applies to
various systems in the Hubbard model family as well as to
relativistic fermions. Here it is illustrated for
nonrelativistic lattice fermions. A configuration of fermion
world lines is decomposed into clusters that contribute
independently to the fermion permutation sign. A cluster
whose flip changes the sign is referred to as a meron.
Configurations containing meron clusters contribute 0 to the
path integral, while all other configurations contribute 1.
The cluster representation describes the partition function
as a gas of clusters in the zero-meron sector.},
Key = {fds245741}
}

@article{fds303655,
Author = {Chandrasekharan, S},
Title = {Ginsparg-Wilson Fermions: A study in the Schwinger
Model},
Journal = {Phys.Rev. D},
Volume = {59},
Pages = {094502},
Year = {1998},
Month = {October},
url = {http://arxiv.org/abs/hep-lat/9810007v2},
Abstract = {Qualitative features of Ginsparg-Wilson fermions, as
formulated by Neuberger, coupled to two dimensional U(1)
gauge theory are studied. The role of the Wilson mass
parameter in changing the number of massless flavors in the
theory and its connection with the index of the Dirac
operator is studied. Although the index of the Dirac
operator is not related to the geometric definition of the
topological charge for strong couplings, the two start to
agree as soon as one goes to moderately weak couplings. This
produces the desired singularity in the quenched chiral
condensate which appears to be very difficult to reproduce
with staggered fermions. The fermion determinant removes the
singularity and reproduces the known chiral condensate and
the meson mass within understandable errors.},
Doi = {10.1103/PhysRevD.59.094502},
Key = {fds303655}
}

@article{Beard:1997ic,
Author = {Beard, B. B. and others},
Title = {D-theory: Field theory via dimensional reduction of discrete
variables},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {63},
Pages = {775-789},
Year = {1998},
url = {http://arxiv.org/pdf/hep-lat/9709120},
Abstract = {http://arxiv.org/abs/hep-lat/9709120},
Key = {Beard:1997ic}
}

@article{Brower:1998kg,
Author = {Brower, R. and Chandrasekharan, S. and Wiese, U.
J.},
Title = {Green's functions from quantum cluster algorithms},
Journal = {Physica A},
Volume = {261},
Pages = {520},
Year = {1998},
url = {http://arxiv.org/pdf/cond-mat/9801003},
Abstract = {http://arxiv.org/abs/cond-mat/9801003},
Key = {Brower:1998kg}
}

@article{Orginos:1997fh,
Author = {Orginos, K. and Bietenholz, W. and Brower, R. and Chandrasekharan, S. and Wiese, U. -J.},
Title = {The perfect quark-gluon vertex function},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {63},
Pages = {904-906},
Year = {1998},
url = {http://arxiv.org/pdf/hep-lat/9709100},
Abstract = {http://arxiv.org/abs/hep-lat/9709100},
Key = {Orginos:1997fh}
}

@article{fds245666,
Author = {Brower, R and Chandrasekharan, S and Wiese, U-J},
Title = {Green’s functions from quantum cluster algorithms11This
work is supported in part by funds provided by the US
Department of Energy (DOE) under cooperative research
agreement DE-FC02-94ER40818.},
Volume = {261},
Number = {3},
Pages = {520-533},
Year = {1998},
Abstract = {We show that cluster algorithms for quantum models have a
meaning independent of the basis chosen to construct them.
Using this idea, we propose a new method for measuring with
little effort a whole class of Green’s functions, once a
cluster algorithm for the partition function has been
constructed. To explain the idea, we consider the quantum XY
model and compute its two point Green’s function in
various ways, showing that all of them are equivalent. We
also provide numerical evidence confirming the analytic
arguments. Similar techniques are applicable to other
models. In particular, in the recently constructed quantum
link models, the new technique allows us to construct
improved estimators for Wilson loops and may lead to a very
precise determination of the glueball spectrum.},
Key = {fds245666}
}

@article{fds245724,
Author = {Beard, BB and Brower, RC and Chandrasekharan, S and Chen, D and Tsapalis, A and Wiese, U-J},
Title = {D-theory: Field theory via dimensional reduction of discrete
variables},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {63},
Number = {1-3},
Pages = {775-789},
Year = {1998},
Abstract = {A new non-perturbative approach to quantum field theory -
D-theory - is proposed, in which continuous classical fields
are replaced by discrete quantized variables which undergo
dimensional reduction. The 2-d classical O(3) model emerges
from the (2 + 1)-d quantum Heisenberg model formulated in
terms of quantum spins. Dimensional reduction is
demonstrated explicitly by simulating correlation lengths up
to 350,000 lattice spacings using a loop cluster algorithm.
In the framework of D-theory, gauge theories are formulated
in terms of quantum links - the gauge analogs of quantum
spins. Quantum links are parallel transporter matrices whose
elements are non-commuting operators. They can be expressed
as bilinears of anticommuting fermion constituents. In
quantum link models dimensional reduction to four dimensions
occurs, due to the presence of a 5-d Coulomb phase, whose
existence is confirmed by detailed simulations using
standard lattice gauge theory. Using Shamir's variant of
Kaplan's fermion proposal, in quantum link QCD quarks appear
as edge states of a 5-d slab. This naturally protects their
chiral symmetries without fine-tuning. The first efficient
cluster algorithm for a gauge theory with a continuous gauge
group is formulated for the U(1) quantum link model.
Improved estimators for Wilson loops are constructed, and
dimensional reduction to ordinary lattice QED is verified
numerically.},
Key = {fds245724}
}

@article{fds245725,
Author = {Orginos, K and Bietenholz, W and Brower, R and Chandrasekharan, S and Wiese, U-J},
Title = {The perfect Quark-Gluon vertex function},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {63},
Number = {1-3},
Pages = {904-906},
Year = {1998},
Abstract = {We evaluate a perfect quark-gluon vertex function for QCD in
coordinate space and truncate it to a short range. We
present preliminary results for the charmonium spectrum
using this quasi-perfect action.},
Key = {fds245725}
}

@article{fds245737,
Author = {Brower, R and Chandrasekharan, S and Wiese, U-J},
Title = {Green's functions from quantum cluster algorithms},
Journal = {Physica A: Statistical Mechanics and its
Applications},
Volume = {261},
Number = {3-4},
Pages = {520-533},
Year = {1998},
Abstract = {We show that cluster algorithms for quantum models have a
meaning independent of the basis chosen to construct them.
Using this idea, we propose a new method for measuring with
little effort a whole class of Green's functions, once a
cluster algorithm for the partition function has been
constructed. To explain the idea, we consider the quantum XY
model and compute its two point Green's function in various
ways, showing that all of them are equivalent. We also
provide numerical evidence confirming the analytic
arguments. Similar techniques are applicable to other
models. In particular, in the recently constructed quantum
link models, the new technique allows us to construct
improved estimators for Wilson loops and may lead to a very
precise determination of the glueball spectrum. © 1998
reserved.},
Key = {fds245737}
}

@article{fds303654,
Author = {Brower, R and Chandrasekharan, S and Wiese, U-J},
Title = {QCD as a Quantum Link Model},
Journal = {Phys. Rev. D},
Volume = {60},
Pages = {094502},
Year = {1997},
Month = {April},
url = {http://arxiv.org/abs/hep-th/9704106v1},
Abstract = {QCD is constructed as a lattice gauge theory in which the
elements of the link matrices are represented by
non-commuting operators acting in a Hilbert space. The
resulting quantum link model for QCD is formulated with a
fifth Euclidean dimension, whose extent resembles the
inverse gauge coupling of the resulting four-dimensional
theory after dimensional reduction. The inclusion of quarks
is natural in Shamir's variant of Kaplan's fermion method,
which does not require fine-tuning to approach the chiral
limit. A rishon representation in terms of fermionic
constituents of the gluons is derived and the quantum link
Hamiltonian for QCD with a U(N) gauge symmetry is expressed
in terms of glueball, meson and constituent quark operators.
The new formulation of QCD is promising both from an
analytic and from a computational point of
view.},
Doi = {10.1103/PhysRevD.60.094502},
Key = {fds303654}
}

@article{Bietenholz:1997kr,
Author = {Bietenholz, W. and Brower, R. and Chandrasekharan, S. and Wiese, U. J.},
Title = {Perfect lattice topology: The quantum rotor as a test
case},
Journal = {Phys. Lett. B},
Volume = {407},
Pages = {283-289},
Year = {1997},
url = {http://arxiv.org/pdf/hep-lat/9704015},
Abstract = {http://arxiv.org/abs/hep-lat/9704015},
Key = {Bietenholz:1997kr}
}

@article{Bietenholz:1996qc,
Author = {Bietenholz, W. and Brower, R. and Chandrasekharan, S. and Wiese, U. J.},
Title = {Perfect lattice actions for staggered fermions},
Journal = {Nucl. Phys. B},
Volume = {495},
Pages = {285-305},
Year = {1997},
url = {http://arxiv.org/pdf/hep-lat/9612007},
Abstract = {http://arxiv.org/abs/hep-lat/9612007},
Key = {Bietenholz:1996qc}
}

@article{Chandrasekharan:1996ih,
Author = {Chandrasekharan, S. and Wiese, U. J.},
Title = {Quantum link models: A discrete approach to gauge
theories},
Journal = {Nucl. Phys. B},
Volume = {492},
Pages = {455-474},
Year = {1997},
url = {http://arxiv.org/pdf/hep-lat/9609042},
Abstract = {http://arxiv.org/abs/hep-lat/9609042},
Key = {Chandrasekharan:1996ih}
}

@article{Bietenholz:1996pf,
Author = {Bietenholz, W. and Brower, R. and Chandrasekharan, S. and Wiese, U. J.},
Title = {Progress on perfect lattice actions for QCD},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {53},
Pages = {921-934},
Year = {1997},
url = {http://arxiv.org/pdf/hep-lat/9608068},
Abstract = {http://arxiv.org/abs/hep-lat/9608068},
Key = {Bietenholz:1996pf}
}

@article{Chandrasekharan:1996en,
Author = {Chandrasekharan, Shailesh},
Title = {A large N chiral transition on a plaquette},
Journal = {Phys. Lett. B},
Volume = {395},
Pages = {83-88},
Year = {1997},
url = {http://arxiv.org/pdf/hep-th/9610225},
Abstract = {http://arxiv.org/abs/hep-th/9610225},
Key = {Chandrasekharan:1996en}
}

@article{fds245726,
Author = {Bietenholz, W and Brower, R and Chandrasekharan, S and Wiese,
U-J},
Title = {Perfect lattice topology: The quantum rotor as a test
case},
Journal = {Physics Letters, Section B: Nuclear, Elementary Particle and
High-Energy Physics},
Volume = {407},
Number = {3-4},
Pages = {283-289},
Year = {1997},
Abstract = {Lattice actions and topological charges that are classically
and quantum mechanically perfect (i.e. free of lattice
artifacts) are constructed analytically for the quantum
rotor. It is demonstrated that the Manton action is
classically perfect while the Villain action is quantum
perfect. The geometric construction for the topological
charge is only perfect at the classical level. The quantum
perfect lattice topology associates a topological charge
distribution, not just a single charge, with each lattice
field configuration. For the quantum rotor with the
classically perfect action and topological charge, the
remaining cut-off effects are exponentially suppressed. ©
Key = {fds245726}
}

@article{fds245727,
Author = {Bietenholz, W and Brower, R and Chandrasekharan, S and Wiese,
U-J},
Title = {Perfect lattice actions for staggered fermions},
Journal = {Nuclear Physics B},
Volume = {495},
Number = {1-2},
Pages = {285-305},
Year = {1997},
Abstract = {We construct a perfect lattice action for staggered fermions
by blocking from the continuum. The locality, spectrum and
pressure of such perfect staggered fermions are discussed.
gauge fields and discuss its locality as well as the
resulting static quark-antiquark potential. This provides a
basis for the construction of (classically) perfect lattice
actions for QCD using staggered fermions. © 1997 Elsevier
Science B.V.},
Key = {fds245727}
}

@article{fds245728,
Author = {Chandrasekharan, S},
Title = {A large N chiral transition on a plaquette},
Journal = {Physics Letters, Section B: Nuclear, Elementary Particle and
High-Energy Physics},
Volume = {395},
Number = {1-2},
Pages = {83-88},
Year = {1997},
Abstract = {We construct a model of a chiral transition using the well
known large N transition in two dimensional U(N) lattice
gauge theory. Restricting the model to a single plaquette,
we introduce Grassmann variables on the corners of the
plaquette with the natural phase factors of staggered
fermions and couple them to the U(N) link variables. The
classical theory has a continuous chiral symmetry which is
broken at strong couplings, but is restored for weak
couplings in the N → ∞ limit. * This work is supported
in part by funds provided by the U.S. Department of Energy
(D.O.E.) under cooperative research agreement
#DF-FC02-94ER40818.},
Key = {fds245728}
}

@article{fds245729,
Author = {Chandrasekharan, S and Wiese, U-J},
Title = {Quantum link models: A discrete approach to gauge
theories},
Journal = {Nuclear Physics B},
Volume = {492},
Number = {1-2},
Pages = {455-471},
Year = {1997},
Abstract = {We construct lattice gauge theories in which the elements of
the link matrices are represented by non-commuting operators
acting in a Hubert space. These quantum link models are
related to ordinary lattice gauge theories in the same way
as quantum spin models are related to ordinary classical
spin systems. Here U (1) and SU (2) quantum link models are
constructed explicitly. As Hamiltonian theories quantum link
models are non-relativistic gauge theories with potential
applications in condensed matter physics. When formulated
with a fifth Euclidean dimension, universality arguments
suggest that dimensional reduction to four dimensions
occurs. Hence, quantum link models are also reformulations
of ordinary quantum field theories and are applicable to
particle physics, for example to QCD. The configuration
space of quantum link models is discrete and hence their
numerical treatment should be simpler than that of ordinary
lattice gauge theories with a continuous configuration
B.V.},
Key = {fds245729}
}

@article{fds245730,
Author = {Bietenholz, W and Brower, R and Chandrasekharan, S and Wiese,
U-J},
Title = {Progress on perfect lattice actions for QCD},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {53},
Number = {1-3},
Pages = {921-934},
Year = {1997},
Abstract = {We describe a number of aspects in our attempt to construct
an approximately perfect lattice action for QCD. Free quarks
are made optimally local on the whole renormalized
trajectory and their couplings are then truncated by
imposing 3-periodicity. The spectra of these short ranged
fermions are excellent approximations to continuum spectra.
corresponding perfect quark-gluon vertex function,
identifying in particular the "perfect clover term". First
simulations for heavy quarks show that the mass is strongly
renormalized, but again the renormalized theory agrees very
well with continuum physics. Furthermore we describe the
multigrid formulation for the non-perturbative perfect
action and we present the concept of an exactly (quantum)
perfect topological charge on the lattice.},
Key = {fds245730}
}

@article{fds245731,
Author = {Chandrasekharan, S and Huang, S},
Title = {Z3 twisted chiral condensates in QCD at finite
temperatures.},
Journal = {Physical Review D: Particles, Fields, Gravitation and
Cosmology},
Volume = {53},
Number = {9},
Pages = {5100-5104},
Year = {1996},
Month = {May},
ISSN = {0556-2821},
url = {http://www.ncbi.nlm.nih.gov/pubmed/10020507},
Abstract = {It was recently observed in a lattice QCD measurement that
the chiral condensate in the quenched approximation shows
dramatically different behavior in the three Z3-equivalent
deconfined phases. We argue that this phenomenon can be
understood qualitatively as an effect of Z3 twists on
fermionic fields. Quarks under these Z3 twists become global
anyons and, hence, display different thermodynamic
properties. We further show that the lattice data can be
roughly modeled by a Nambu-Jona-Lasinio-type Lagrangian with
a minimal coupling to a constant gauge field A0=2Ï€nT/3
(with n=0,Â±1), which arises naturally from the nontrivial
phase of the Polyakov line.},
Key = {fds245731}
}

@article{Chandrasekharan:1995gt,
Author = {Chandrasekharan, Shailesh and Christ, Norman
H.},
Title = {Dirac Spectrum, Axial Anomaly and the QCD Chiral Phase
Transition},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {47},
Pages = {527-534},
Year = {1996},
url = {http://arxiv.org/pdf/hep-lat/9509095},
Abstract = {http://arxiv.org/abs/hep-lat/9509095},
Key = {Chandrasekharan:1995gt}
}

@article{fds245732,
Author = {Chandrasekharan, S and Christ, N},
Title = {Dirac spectrum, axial anomaly and the QCD chiral phase
transition},
Journal = {Nuclear Physics B - Proceedings Supplements},
Volume = {47},
Number = {1-3},
Pages = {527-534},
Year = {1996},
url = {http://dx.doi.org/10.1016/0920-5632(96)00115-6},
Abstract = {The QCD phase transition is studied on 163 and 323 × 4
lattices both with and without quark loops. We introduce a
new zero-flavor or quenched species of quark ζ and study
the resulting chiral condensate, ζ̄ζ as a function of the
ζ mass, mζ. By examining ζ̄ζ for 10-10 ≤ mζ ≤ 10
we gain considerable information about the spectrum of Dirac
eigenvalues. A comparison of ma = 0.01 and 0.025 shows
little dependence of the Dirac spectrum on such a light,
dynamical quark mass, after an overall shift in β is
removed. The presence of sufficient small eigenvalues to
support anomalous chiral symmetry breaking in the high
temperature phase is examined quantitatively. In an effort
to enhance these small eigenvalues, ζ̄ζ is also examined
in the pure gauge theory in the region of the deconfinement
transition with unexpected results. Above the critical
temperature, the three Z3 phases show dramatically different
chiral behavior. Surprisingly, the real phase shows chiral
symmetry, suggesting that a system with one flavor of
staggered fermion at Nt = 4 will possess a chiral a phase
transition - behavior not expected in the continuum
limit.},
Doi = {10.1016/0920-5632(96)00115-6},
Key = {fds245732}
}

@article{Chandrasekharan:1995nf,
Author = {Chandrasekharan, S and Huang, S},
Title = {Z3 twisted chiral condensates in QCD at finite
temperatures},
Journal = {Physical Review D - Particles, Fields, Gravitation and
Cosmology},
Volume = {53},
Number = {9},
Pages = {5100-5104},
Year = {1996},
url = {http://arxiv.org/pdf/hep-ph/9512323},
Abstract = {It was recently observed in a lattice QCD measurement that
the chiral condensate in the quenched approximation shows
dramatically different behavior in the three Z3-equivalent
deconfined phases. We argue that this phenomenon can be
understood qualitatively as an effect of Z3 twists on
fermionic fields. Quarks under these Z3 twists become global
anyons and, hence, display different thermodynamic
properties. We further show that the lattice data can be
roughly modeled by a Nambu-Jona-Lasinio-type Lagrangian with
a minimal coupling to a constant gauge field A0=2πnT/3
(with n=0,±1), which arises naturally from the nontrivial
phase of the Polyakov line.},
Key = {Chandrasekharan:1995nf}
}

@article{Chandrasekharan:1994cq,
Author = {Chandrasekharan, Shailesh},
Title = {Critical behavior of the chiral condensate at the QCD phase
transition},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {42},
Pages = {475-477},
Year = {1995},
url = {http://arxiv.org/pdf/hep-lat/9412070},
Abstract = {http://arxiv.org/abs/hep-lat/9412070},
Key = {Chandrasekharan:1994cq}
}

@article{fds245734,
Author = {Chandrasekharan, S},
Title = {Critical behavior of the chiral condensate at the QCD phase
transition},
Journal = {Nuclear Physics, Section B: Proceedings Supplements},
Volume = {42},
Number = {1-3},
Pages = {475-477},
Year = {1995},
ISSN = {0920-5632},
url = {http://dx.doi.org/10.1016/0920-5632(95)00284-G},
Abstract = {We study the critical behavior of the chiral condensate near
the QCD phase transition in the background of two fixed
light dynamical (sea) quarks. We study the condensate for
5.245 ≤ β ≤ 5.3 and 10-10 ≤ mval ≤ 10 (in lattice
units) on a 163 × 4 lattice using staggered fermions with
msea fixed at 0.01. © 1995 Elsevier Science B.V. All rights
reserved.},
Doi = {10.1016/0920-5632(95)00284-G},
Key = {fds245734}
}

@article{fds245735,
Author = {Chandrasekharan, S},
Title = {Anomaly cancellation in 2+1 dimensions in the presence of a
domain wall mass.},
Journal = {Physical Review D: Particles, Fields, Gravitation and
Cosmology},
Volume = {49},
Number = {4},
Pages = {1980-1987},
Year = {1994},
Month = {February},
ISSN = {0556-2821},
url = {http://www.ncbi.nlm.nih.gov/pubmed/10017182},
Abstract = {A fermion in 2+1 dimensions, with a mass function which
depends on one spatial coordinate and passes through a zero
(a domain wall mass), in the background of an Abelian gauge
field is considered. In this model, originally proposed in a
non-Abelian version by Callan and Harvey, the gauge
variation of the effective gauge action mainly consists of
two terms. One comes from the induced Chern-Simons term and
the other from the chiral fermions, bound to the
(1+1)-dimensional wall, and they are expected to cancel each
other. Though there exist arguments in favor of this, based
on the possible forms of the effective action valid far from
the wall and some facts about theories of chiral fermions in
1+1 dimensions, a complete calculation is lacking. In this
paper we present an explicit calculation of this
cancellation at one loop which is valid even close to the
wall. We show that integrating out the massive'' modes of
the theory does produce the Chern-Simons term, as
appreciated previously. In addition, we show that it
generates a term that softens the high energy behavior of
the (1+1)-dimensional effective chiral theory thereby
resolving an ambiguity present in a general
(1+1)-dimensional theory.},
Key = {fds245735}
}

@article{Chandrasekharan:1993ag,
Author = {Chandrasekharan, Shailesh},
Title = {Anomaly cancellation in (2+1)-dimensions in the presence of
a domain wall mass},
Journal = {Phys. Rev. D},
Volume = {49},
Pages = {1980-1987},
Year = {1994},
url = {http://arxiv.org/pdf/hep-th/9311050},
Abstract = {http://arxiv.org/abs/hep-th/9311050},
Key = {Chandrasekharan:1993ag}
}

@article{Chandrasekharan:1994ae,
Author = {Chandrasekharan, S.},
Title = {Fermions with a domain wall mass: Explicit Greens function
and anomaly cancellation},
Journal = {Nucl. Phys. Proc. Suppl.},
Volume = {34},
Pages = {579-582},
Year = {1994},
Key = {Chandrasekharan:1994ae}
}

@article{fds245733,
Author = {Chandrasekharan, S},
Title = {Fermions with a domain-wall mass: explicit greens function
and anomaly cancellation},
Journal = {Nuclear Physics, Section B: Proceedings Supplements},
Volume = {34},
Number = {C},
Pages = {579-582},
Year = {1994},
ISSN = {0920-5632},
Abstract = {We calculate the explicit Greens function for fermions in
2+1 dimensions, with a domain wall mass. We then show a
calculation demonstrating the anomaly cancellation when such
fermions move in the background of an abelian gauge field.
Key = {fds245733}
}

%% Papers Accepted
@article{fds225572,
Author = {Haiyuan Zou and Yuzhi Liu and Chen-Yen Lai and J. Unmuth-Yockey and A.
Bazavov, Z.Y. Xie and T. Xiang and S. Chandrasekharan and S. -W.
Tsai, Y. Meurice},
Title = {Towards quantum computing for the classical O(2)
model},
Journal = {Phys. Rev. A},
Year = {2014},
url = {http://arxiv.org/abs/arXiv:1403.5238},
Abstract = {http://arxiv.org/abs/arXiv:1403.5238},
Key = {fds225572}
}

%% Papers Submitted
@article{fds225571,
Author = {V. Ayyar and S. Chandrasekharan},
Title = {Massive fermions without fermion bilinear
condensates},
Journal = {arXiv:1410.6474 (submitted to Phys. Rev.
D)},
Year = {2014},
Month = {October},
url = {http://arxiv.org/abs/arXiv:1410.6474},
Abstract = {http://arxiv.org/abs/arXiv:1410.6474},
Key = {fds225571}
}

@article{fds303637,
Author = {Chandrasekharan, S},
Title = {Fermion bags and a new origin for a fermion
mass},
Journal = {PoS - Proceedings of Science},
Volume = {Part F130500},
Year = {2014},
Month = {January},
url = {http://arxiv.org/abs/1412.3532v1},
Abstract = {© Copyright owned by the author(s) under the terms of the
Licence. The fermion bag is a powerful idea that helps to
solve fermion lattice field theories using Monte Carlo
methods. Some sign problems that had remained unsolved
earlier can be solved within this framework. In this work we
argue that the fermion bag also gives insight into a new
mechanism of fermion mass generation, especially at strong
couplings where fermion masses are related to the fermion
bag size. On the other hand, chiral condensates arise due to
zero modes in the Dirac operator within a fermion bag.
Although in traditional four-fermion models the two
quantities seem to be related, we show that they can be
decoupled. While fermion bags become small at strong
couplings, the ability of zero modes of the Dirac operator
within fermion bags to produce a chiral condensate, can be
suppressed by the presence of additional zero modes from
other fermions. Thus, fermions can become massive even
without a chiral condensate. This new mechanism of mass
generation was discovered long ago in lattice field theory,
but has remained unappreciated. Recent work suggests that it
may be of interest even in continuum quantum field
theory.},
Key = {fds303637}
}

@article{fds303651,
Author = {Lee, J-W and Chandrasekharan, S and Baranger, HU},
Title = {Disorder-Induced Superfluidity in Hardcore Bosons in Two
Dimensions},
Year = {2006},
Month = {November},
url = {http://arxiv.org/abs/cond-mat/0611109v1},
Abstract = {We study the effect of disorder on hardcore bosons in two
dimensions at the SU(2) symmetric Heisenberg point''. We
obtain our results with quantum Monte Carlo simulations
using the directed loop algorithm. In the absence of
disorder, the system has no long-range order at finite
temperature due to the enhanced symmetry. However, the
introduction of a disordered potential, uniformly
distributed from -D to D, induces a finite-temperature
superfluid phase. In particular the diagonal correlation
length \xi decreases but the superfluid order-parameter
correlation function becomes a power-law. A non-monotonic
finite-size behavior is noted and explained as arising due
to \xi. We provide evidence that at long distances the
effects of a weak disordered potential can be mimicked by an
effective uniform potential with a root-mean-square value:
mu_eff = D/sqrt{3}. For strong disorder, the system becomes
a Bose glass insulator.},
Key = {fds303651}
}

%% Preprints
@article{fds212507,
Author = {S. Chandrasekharan and U.-J. Wiese},
Title = {Partition Functions of Strongly Correlated Electron Systems
as 'Fermionants'.},
Journal = {arXiv:1108.2461},
Year = {2011},
Month = {July},
url = {http://arxiv.org/abs/arXiv:1108.2461},
Abstract = {We introduce a new mathematical object, the "fermionant"
${\mathrm{Ferm}}_N(G)$, of type $N$ of an $n \times n$
matrix $G$. It represents certain $n$-point functions
involving $N$ species of free fermions. When N=1, the
fermionant reduces to the determinant. The partition
function of the repulsive Hubbard model, of geometrically
frustrated quantum antiferromagnets, and of Kondo lattice
models can be expressed as fermionants of type N=2, which
naturally incorporates infinite on-site repulsion. A
computation of the fermionant in polynomial time would solve
many interesting fermion sign problems.},
Key = {fds212507}
}

@article{fds4134,
Author = {S. Chandrasekharan and U.-J. Wiese},
Title = {SO(10) UNIFICATION OF COLOR SUPERCONDUCTIVITY AND CHIRAL
SYMMETRY BREAKING?},
Year = {2000},
Abstract = {Motivated by the SO(5) theory of high-temperature
superconductivity and antiferromagnetism, we ask if an
SO(10) theory unifies color superconductivity and chiral
symmetry breaking in QCD. The transition to the color
superconducting phase would then be analogous to a spin flop
transition. While the spin flop transition generically has a
unified SO(3) description, the SO(5) and SO(10) symmetric
fixed points are unstable, at least in (4 - epsilon)
dimensions, and require the fine-tuning of one additional
relevant parameter. If QCD is near the SO(10) fixed point,
it has interesting consequences for heavy ion collisions and
neutron stars.},
Key = {fds4134}
}

@article{fds4139,
Author = {S. Chandrasekharan and B. Scarlet and U.-J.
Wiese},
Title = {MERON CLUSTER SIMULATION OF QUANTUM SPIN LADDERS IN A
MAGNETIC FIELD},
Year = {1999},
Key = {fds4139}
}