%% Papers Published
@article{fds152773,
Author = {Sean Fleming and Thomas Mehen},
Title = {Hadronic Decays of the X(3872) to chi_{cJ} in Effective
Field Theory},
Journal = {Phys. Rev. D78:094019},
Year = {2008},
url = {http://arXiv.org/abs/0807.2674v2},
Abstract = {The decays of the X(3872) to P-wave quarkonia are calculated
under the assumption that it is a shallow bound state of
neutral charmed mesons. The X(3872) is described using an
effective theory of nonrelativistic D mesons and pions
(X-EFT). We calculate X(3872) decays by first matching heavy
hadron chiral perturbation theory (HHchiPT) amplitudes for
D^0 bar{D}^{*0} -> chi_{cJ} + (pi^0,pi+pi) onto local
operators in X-EFT, and then using these operators to
calculate the X(3872) decays. This procedure reproduces the
factorization theorems for X(3872) decays to conventional
quarkonia previously derived using the operator product
expansion. For single pion decays, we find nontrivial
dependence on the pion energy from HHchiPT diagrams with
virtual D mesons. This nontrivial energy dependence can
potentially modify heavy quark symmetry predictions for the
relative sizes of decay rates. At leading order, decays to
final states with two pions are dominated by the final state
chi_{c1} + pi^0 + pi^0, with a branching fraction just below
that for the decay to chi_{c1} + pi^0. Decays to all other
final states with two pions are highly suppressed.},
Key = {fds152773}
}
@article{fds152771,
Author = {Chul Kim and Adam K. Leibovich and Thomas Mehen},
Title = {Nonperturbative Charming Penguin Contributions to Isospin
Asymmetries in Radiative B decays},
Journal = {Phys. Rev. D78:054024},
Year = {2008},
url = {http://arXiv.org/abs/0805.1735},
Abstract = {Recent experimental data on the radiative decays B -> V
gamma, where V is a light vector meson, find small isospin
violation in B -> K^* gamma while isospin asymmetries in B
-> rho gamma are of order 20%, with large uncertainties.
Using Soft-Collinear Effective Theory, we calculate isospin
asymmetries in these radiative B decays up to O(1/m_b), also
including O(v alpha_s) contributions from nonperturbative
charming penguins (NPCP). In the absence of NPCP
contributions, the theoretical predictions for the
asymmetries are a few percent or less. Including the NPCP
can significantly increase the isospin asymmetries for both
B -> V gamma modes. We also consider the effect of the NPCP
on the branching ratio and CP asymmetries in B^\pm -> V^\pm
gamma.},
Key = {fds152771}
}
@article{fds152772,
Author = {Thomas Mehen},
Title = {On non-relativistic conformal field theory and trapped
atoms: Virial theorems and the state-operator correspondence
in three dimensions},
Journal = {Phys. Rev. A 78, 013614},
Year = {2008},
url = {http://arXiv.org/abs/0712.0867},
Abstract = {The field theory of nonrelativistic fermions interacting via
contact interactions can be used to calculate the properties
of few-body systems of cold atoms confined in harmonic
traps. The state-operator correspondence of Non-Relativistic
Conformal Field Theory (NRCFT) shows that the energy
eigenvalues (in oscillator units) of N harmonically trapped
fermions can be calculated from the scaling dimensions of
N-fermion operators in the NRCFT. They are also in
one-to-one correspondence with zero-energy, scale-invariant
solutions to the N-body problem in free space. We show that
these two mappings of the trapped fermion problem to free
space problems are related by an automorphism of the SL(2,R)
algebra of the conformal symmetry of fermions at the unitary
limit. This automorphism exchanges the internal Hamiltonian
of the gas with the trapping potential and hence provides a
novel method for deriving virial theorems for trapped Fermi
gases at the unitary limit. We also show that the
state-operator correspondence can be applied directly in
three spatial dimensions by calculating the scaling
dimensions of two- and three-fermion operators and finding
agreement with known exact results for energy levels of two
and three trapped fermions at the unitary
limit.},
Key = {fds152772}
}
@article{fds140354,
Author = {A. Idilbi and T. Mehen},
Title = {On the equivalence of soft and zero-bin subtractions},
Journal = {Phys.Rev.D75:114017},
Year = {2007},
url = {http://arXiv.org/abs/hep-ph/0702022},
Abstract = {Zero-bin subtractions are required to avoid double counting
soft contributions in collinear loop integrals in
Soft-Collinear Effective Theory (SCET). In traditional
approaches to factorization, double counting is avoided by
dividing jet functions by matrix elements of soft Wilson
lines. In this paper, we compare the two approaches to
double counting, studying the quark form factor and deep
inelastic scattering (DIS) as x_B \to 1 as examples. We
explain how the zero-bin subtractions in SCET are required
to reproduce the well-established factorization theorem for
DIS as x_B \to 1. We study one-loop virtual contributions to
the quark form factor and real gluon emission diagrams in
DIS. The two approaches to double counting are equivalent if
dimensional regularization (DR) is used to regulate infrared
(IR) divergences. We discuss in detail ambiguities in the
calculation of one-loop scaleless integrals in DR in SCET
and perturbative QCD. We also demonstrate a nontrivial check
of the equivalence of the zero-bin subtraction and the soft
Wilson line subtraction in the virtual two-loop Abelian
contributions to the quark form factor.},
Key = {fds140354}
}
@article{fds140355,
Author = {A. Idilbi and T. Mehen},
Title = {Equivalence of soft and zero-bin subtractions at two
loops},
Journal = {Phys.Rev.D76:094015},
Year = {2007},
url = {http://arXiv.org/abs/0707.1101},
Abstract = {Calculations of collinear correlation functions in
perturbative QCD and Soft-Collinear Effective Theory (SCET)
require a prescription for subtracting soft or zero-bin
contributions in order to avoid double counting the
contributions from soft modes. At leading order in
$\lambda$, where $\lambda$ is the SCET expansion parameter,
the zero-bin subtractions have been argued to be equivalent
to convolution with soft Wilson lines. We give a proof of
the factorization of naive collinear Wilson lines that is
crucial for the derivation of the equivalence. We then check
the equivalence by computing the non-Abelian two-loop mixed
collinear-soft contribution to the jet function in the quark
form factor. These results provide strong support for the
equivalence, which can be used to give a nonperturbative
definition of the zero-bin subtraction at lowest order in
$\lambda$.},
Key = {fds140355}
}
@article{fds140356,
Author = {S. Fleming and M. Kusunoki and T. Mehen and U. van
Kolck},
Title = {Pion Interactions in the X(3872)},
Journal = {Phys.Rev.D76:034006},
Year = {2007},
url = {http://arXiv.org/abs/hep-ph/0703168},
Abstract = {We consider pion interactions in an effective field theory
of the narrow resonance X(3872), assuming it is a weakly
bound molecule of the charm mesons D^{0} \bar D^{*0} and
D^{*0} \bar D^{0}. Since the hyperfine splitting of the
D^{0} and D^{*0} is only 7 MeV greater than the neutral pion
mass, pions can be produced near threshold and are
non-relativistic. We show that pion exchange can be treated
in perturbation theory and calculate the
next-to-leading-order correction to the partial decay width
\Gamma[X \to D^0 \bar D^{0} \pi^0].},
Key = {fds140356}
}
@article{fds51597,
Author = {T. Mehen and B. C. Tiburzi},
Title = {Doubly Heavy Baryons and Quark-Diquark Symmetry in Quenched
and Partially Quenched Chiral Perturbation
Theory},
Journal = {Phys. Rev. D74, 054505},
Year = {2006},
url = {http://arxiv.org/abs/hep-lat/0607023},
Abstract = {We extend the chiral Lagrangian with heavy quark-diquark
symmetry to quenched and partially quenched theories. These
theories are used to derive formulae for the chiral
extrapolation of masses and hyperfine splittings of doubly
heavy baryons in lattice QCD simulations. A quark-diquark
symmetry prediction for the hyperfine splittings of heavy
mesons and doubly heavy baryons is rather insensitive to
chiral corrections in both quenched and partially quenched
QCD. Extrapolation formulae for the doubly heavy baryon
electromagnetic transition moments are also determined for
the partially quenched theory.},
Key = {fds51597}
}
@article{fds51598,
Author = {S. Fleming and A. Leibovich and T. Mehen},
Title = {Resummation of Large Endpoint Corrections to Color-Octet
J/\psi Photoproduction},
Journal = {Phys. Rev. D74, 114004},
Year = {2006},
url = {http://arxiv.org/abs/hep-ph/0607121},
Abstract = {An unresolved problem in J/psi phenomenology is a systematic
understanding of the differential photoproduction cross
section, dsigma/dz [gamma + p -> J/psi + X], where z=
E_psi/E_gamma in the proton rest frame. In the
non-relativistic QCD (NRQCD) factorization formalism,
fixed-order perturbative calculations of color-octet
mechanisms suffer from large perturbative and
nonperturbative corrections that grow rapidly in the
endpoint region, z -> 1. In this paper, NRQCD and soft
collinear effective theory are combined to resum these large
corrections to the color-octet photoproduction cross
section. We derive a factorization theorem for the endpoint
differential cross section involving the parton distribution
function and the color-octet J/psi shape functions. A one
loop matching calculation explicitly confirms our
factorization theorem at next-to-leading order. Large
perturbative corrections are resummed using the
renormalization group. The calculation of the color-octet
contribution to dsigma/dz is in qualitative agreement with
data. Quantitative tests of the universality of color-octet
matrix elements require improved knowledge of shape
functions entering these calculations as well as resummation
of the color-singlet contribution which accounts for much of
the total cross section and also peaks near the
endpoint.},
Key = {fds51598}
}
@article{fds43963,
Author = {S. Fleming and T. Mehen},
Title = {Doubly Heavy Baryons, Heavy Quark-Diquark Symmetry and
NRQCD},
Journal = {Phys. Rev. D 73, 034502},
Year = {2006},
url = {http://arxiv.org/abs/hep-ph/0509313},
Abstract = {In the heavy quark limit, properties of heavy mesons and
doubly heavy baryons are related by heavy quark-diquark
symmetry. This problem is reanalyzed in the framework of
Non-Relativistic QCD (NRQCD). We introduce a novel method
for deriving Potential NRQCD (pNRQCD) Lagrangians for
composite fields from vNRQCD, which contains quarks and
antiquarks as explicit degrees of freedom and maintains
manifest power counting in the velocity via a label
formalism. A Hubbard-Stratonovich transformation is used to
eliminate four quark interactions in vNRQCD and then quarks
and antiquarks are integrated out to get effective
Lagrangians for composite fields. This method is used to
rederive Lagrangians for the Q\bar Q and QQ sectors of
pNRQCD and give a correct derivation of the O(1/m_Q)
prediction for the hyperfine splitting of doubly heavy
baryons.},
Key = {fds43963}
}
@article{fds43964,
Author = {J. Hu and T. Mehen},
Title = {Chiral Lagrangian with Heavy Quark-Diquark
Symmetry},
Journal = {Phys. Rev. D 73, 054003},
Year = {2006},
url = {http://arxiv.org/abs/hep-ph/0511321},
Abstract = {We construct a chiral Lagrangian for doubly heavy baryons
and heavy mesons that is invariant under heavy quark-diquark
symmetry at leading order and includes the leading O(1/m_Q)
symmetry violating operators. The theory is used to predict
the electromagnetic decay width of the J=3/2 member of the
ground state doubly heavy baryon doublet. Numerical
estimates are provided for doubly charm baryons. We also
calculate chiral corrections to doubly heavy baryon masses
and strong decay widths of low lying excited doubly heavy
baryons.},
Key = {fds43964}
}
@article{fds43961,
Author = {T. Mehen and B. C. Tiburzi},
Title = {Quarks with Twisted Boundary Conditions in the Epsilon
Regime},
Journal = {Phys. Rev. D72, 014501},
Year = {2005},
url = {http://arxiv.org/abs/hep-lat/0505014},
Abstract = {We study the effects of twisted boundary conditions on the
quark fields in the epsilon regime of chiral perturbation
theory. We consider the $SU(2)_L\times SU(2)_R$ chiral
theory with non-degenerate quarks and the $SU(3)_L\times
SU(3)_R$ chiral theory with massless up and down quarks and
massive strange quarks. The partition function and
condensate are derived for each theory. Because
flavor-neutral Goldstone bosons are unaffected by twisted
boundary conditions chiral symmetry is still restored in
finite volumes. The dependence of the condensate on the
twisting parameters can be used to extract the pion decay
constant from simulations in the epsilon regime. The
relative contribution to the partition function from sectors
of different topological charge is numerically insensitive
to twisted boundary conditions.},
Key = {fds43961}
}
@article{fds43962,
Author = {T. Mehen},
Title = {Excited D_s (and Pentaquarks) in Chiral Perturbation
Theory},
Journal = {Acta. Phys. Polon. B36},
Pages = {2341-2350},
Year = {2005},
url = {http://arxiv.org/abs/hep-ph/0506219},
Abstract = {I present results of a heavy hadron chiral perturbation
theory analysis of the decays and masses of the recently
discovered excited charm mesons. The present data on the
electromagnetic branching ratios are consistent with heavy
quark symmetry predictions and disfavor a molecular
interpretation of these states. I also discuss model
independent predictions for the strong decays of pentaquarks
in the 10-bar representation of SU(3) which can be used to
constrain the angular momentum and parity quantum numbers of
these states.},
Key = {fds43962}
}
@article{fds43965,
Author = {S. Fleming and A. Leibovich and T. Mehen},
Title = {J/Psi Photoproduction at Large z in Soft-Collinear Effective
Theory},
Year = {2005},
url = {http://arxiv.org/abs/hep-ph/0512194},
Abstract = {One of the outstanding problems in J/\psi physics is a
systematic understanding of the differential
photo-production cross section dsigma/dz(gamma + p -> J/psi
+ X), where z= E_psi/E_gamma in the proton rest frame. The
theoretical prediction based on the non-relativistic QCD
(NRQCD) factorization formalism has a color-octet
contribution which grows rapidly in the endpoint region, z
-> 1, spoiling perturbation theory. In addition there are
subleading operators which are enhanced by powers of 1/(1-z)
and they must be resummed to all orders. Here an update of a
systematic analysis is presented. The approach used to
organize the endpoint behavior of the photo-production cross
section is based on a combination of NRQCD and soft
collinear effective theory. While a final result is not yet
available, an intermediate result indicates that better
agreement between theory and data will be achieved in this
framework.},
Key = {fds43965}
}
@article{fds43960,
Author = {T. Mehen and R.P. Springer},
Title = {Even- and Odd-Parity Charmed Meson Masses in Heavy Hadron
Chiral Perturbation Theory},
Journal = {Phys. Rev. D72, 034006},
Year = {2005},
url = {http://arxiv.org/abs/hep-ph/0503134},
Abstract = {We derive mass formulae for the ground state, J^P = 0^- and
1^-, and first excited even-parity, J^P = 0^+ and 1^+,
charmed mesons including one loop chiral corrections and
O(1/m_c) counterterms in heavy hadron chiral perturbation
theory. We show that including these counterterms is
critical for fitting the current data. We find that certain
parameter relations in the parity doubling model are not
renormalized at one loop, providing a natural explanation
for the equality of the hyperfine splittings of ground state
and excited doublets.},
Key = {fds43960}
}
@article{fds29796,
Author = {T. Mehen and C. Schat},
Title = {Determining Pentaquark Quantum Numbers from Strong
Decays},
Journal = {Phys. Lett. B588},
Pages = {67-73},
Year = {2004},
url = {http://arxiv.org/abs/hep-ph/0401107},
Abstract = {Assuming that the recently observed $\Theta^+$ and
$\Xi^{--}$ are members of an anti-decuplet of SU(3), decays
to ground state baryons and mesons are calculated using an
effective Lagrangian which incorporates chiral and SU(3)
symmetry. We consider the possible quantum number
assignments $J^\Pi ={1/2}^\pm,{3/2}^\pm$ and calculate
ratios of partial widths. The branching ratios of exotic
cascades can be used to discriminate between even and odd
parity pentaquarks.},
Key = {fds29796}
}
@article{fds29799,
Author = {T. Mehen and R. P. Springer},
Title = {Heavy-Quark Symmetry and the Electromagnetic Decays of
Excited Charm Strange Mesons},
Journal = {Phys. Rev. D70, 074014},
Year = {2004},
url = {http://arxiv.org/abs/hep-ph/0407181},
Abstract = {Heavy-hadron chiral perturbation theory (HH$\chi$PT) is
applied to the decays of the even-parity charmed strange
mesons, D_{s0}(2317) and D_{s1}(2460). Heavy-quark spin
symmetry predicts the branching fractions for the three
electromagnetic decays of these states to the ground states
D_s and D_s^* in terms of a single parameter. The resulting
predictions for two of the branching fractions are
significantly higher than current upper limits from the CLEO
experiment. Leading corrections to the branching ratios from
chiral loop diagrams and spin-symmetry violating operators
in the HH$\chi$PT Lagrangian can naturally account for this
discrepancy. Finally the proposal that the D_{s0}(2317)
(D_{s1}(2460)) is a hadronic bound state of a D (D^*) meson
and a kaon is considered. Leading order predictions for
electromagnetic branching ratios in this molecular scenario
are in very poor agreement with existing
data.},
Key = {fds29799}
}
@article{fds29849,
Author = {E. Braaten and M. Kusunoki and Y. Jia and T. Mehen},
Title = {$\Lambda_c^+/\Lambda^-_c$ Asymmetry in Hadroproduction for
Heavy-Quark Recombination},
Journal = {Phys. Rev. D70, 054021},
Year = {2004},
url = {http://arxiv.org/abs/hep-ph/0304280},
Abstract = {Asymmetries in the hadroproduction of charm particles
directly probe power corrections to the QCD factorization
theorems. In this paper, the heavy-quark recombination
mechanism, a power correction that explains charm meson
asymmetries, is extended to charm baryons. In this
mechanism, a light quark participates in the hard scattering
that creates a charm quark and they hadronize together into
a charm baryon. This provides a natural and economical
explanation for the \Lambda_c^+/\Lambda_c^- asymmetries
measured in \pi N and p N collisions.},
Key = {fds29849}
}
@article{fds29851,
Author = {Thomas Mehen},
Title = {Recent Developments in Heavy Quark and Quarkonium
Production},
Journal = {Acta Physica Polonica B},
Year = {2003},
url = {http://arxiv.org/abs/hep-ph/0312239},
Abstract = {Recent measurements of J/psi production in e^+ e^- colliders
pose a challenge to the NRQCD factorization theorem for
quarkonium production. Discrepancies between leading order
calculations of color-octet contributions and the momentum
distribution of J/psi observed by Belle and BaBar are
resolved by resumming large perturbative and nonperturbative
corrections that are enhanced near the kinematic endpoint.
The large cross sections for J/psi + c + \bar c and double
quarkonium production remain poorly understood.
Nonperturbative effects in fixed-target hadroproduction of
open charm are also discussed. Large asymmetries in the
production of charm mesons and baryons probe nonperturbative
corrections to the QCD factorization theorem. A power
correction called heavy-quark recombination can economically
explain these asymmetries with a few universal
parameters.},
Key = {fds29851}
}
@article{fds29852,
Author = {Thomas Mehen},
Title = {Charm Production Asymmetries from Heavy-Quark
Recombination},
Journal = {J. Phys. G},
Year = {2003},
url = {http://arxiv.org/abs/hep-ph/0306178},
Abstract = {Charm asymmetries in fixed-target hadroproduction
experiments are sensitive to power corrections to the QCD
factorization theorem for heavy quark production. A power
correction called heavy-quark recombination has recently
been proposed to explain these asymmetries. In heavy-quark
recombination, a light quark or antiquark participates in a
hard scattering which produces a charm-anticharm quark pair.
The light quark or antiquark emerges from the scattering
with small momentum in the rest frame of the charm quark,
and together they hadronize into a charm particle. The cross
section for this process can be calculated within
perturbative QCD up to an overall normalization. Heavy-quark
recombination explains the observed D meson and \Lambda_c
asymmetries with a minimal set of universal nonperturbative
parameters.},
Key = {fds29852}
}
@article{fds17164,
Author = {S. Fleming and A. Leibovich and T. Mehen},
Title = {Resumming the Color-Octet Contribution to $e^+e^- \to J/\psi
+X$},
Journal = {Phys. Rev. D68, 094011},
Year = {2003},
url = {http://arxiv.org/abs/hep-ph/0306139},
Abstract = {Recent observations of the spectrum of J/psi produced in e+
e- collisions at the Upsilon(4S) resonance are in conflict
with fixed-order calculations using the Non-Relativistic QCD
(NRQCD) effective field theory. One problem is that leading
order color-octet mechanisms predict an enhancement of the
cross section for J/psi with maximal energy that is not
observed in the data. However, in this region of phase space
large perturbative corrections (Sudakov logarithms) as well
as enhanced nonperturbative effects are important. In this
paper we use the newly developed Soft-Collinear Effective
Theory (SCET) to systematically include these effects. We
find that these corrections significantly broaden the
color-octet contribution to the J/psi spectrum. Our
calculation employs a one-stage renormalization group
evolution rather than the two-stage evolution used in
previous SCET calculations. We give a simple argument for
why the two methods yield identical results to lowest order
in the SCET power counting.},
Key = {fds17164}
}
@article{fds17162,
Author = {R. Kaiser and A. V. Manohar and T. Mehen},
Title = {Isospin Violation in $e^+ e^- \rightarrow B
\overline{B}$},
Journal = {Phys. Rev. Lett. 90, 142001},
Year = {2003},
url = {http://arxiv.org/abs/hep-ph/0208194},
Abstract = {The ratio of the B+ B- and B0 B0bar production rates in e+
e- annihilation is computed as a function of the B meson
velocity and BB* pi coupling constant, using a
non-relativistic effective field theory.},
Key = {fds17162}
}
@article{fds17161,
Author = {T. Mehen and B. Wecht},
Title = {Gauge Fields and Scalars in Rolling Tachyon
Backgrounds},
Journal = {JHEP 0302},
Pages = {58},
Year = {2003},
url = {http://arxiv.org/abs/hep-th/0206212},
Abstract = {We investigate the dynamics of gauge and scalar fields on
unstable D-branes with rolling tachyons. Assuming an FRW
metric on the brane, we find a solution of the tachyon
equation of motion which is valid for arbitrary tachyon
potentials and scale factors. The equations of motion for a
U(1) gauge field and a scalar field in this background are
derived. These fields see an effective metric which differs
from the original FRW metric. The field equations receive
large corrections due to the curvature of the effective
metric as well as the time variation of the gauge coupling.
The equations of state for these fields resemble those of
nonrelativistic matter rather than massless
particles.},
Key = {fds17161}
}
@article{fds3887,
Author = {E. Braaten and Yu Jia and T. Mehen},
Title = {The Leading Particle Effect From Heavy-Quark
Recombination},
Journal = {Phys. Rev. Lett. 89, 122002},
Year = {2002},
url = {http://arxiv.org/abs/hep-ph/0205149},
Abstract = {The leading particle effect in charm hadroproduction is an
enhancement of the cross section for a charmed hadron D in
the forward direction of the beam when the beam hadron has a
valence parton in common with the D. The large D+/D-
asymmetry observed by the E791 experiment is an example of
this phenomenon. We show that the heavy-quark recombination
mechanism provides an economical explanation for this
effect. In particular, the D+/D- asymmetry can be fit
reasonably well using a single parameter whose value is
consistent with a recent determination from charm
photoproduction.},
Key = {fds3887}
}
@article{fds3892,
Author = {E. Braaten and Yu Jia and T. Mehen},
Title = {Charm Anti-Charm Asymmetries in Photoproduction from
Heavy-Quark Recombination},
Journal = {Phys. Rev. D66, 014003},
Year = {2002},
url = {http://arxiv.org/abs/hep-ph/0111296},
Abstract = {The asymmetries between charm and anticharm mesons observed
in fixed-target photoproduction experiments are an order of
magnitude larger than the asymmetries predicted by
conventional perturbative QCD. We show that these charm
meson asymmetries can be explained by a heavy-quark
recombination mechanism for heavy meson production. In this
process, a charm quark combines with a light antiquark from
the hard-scattering process and they subsequently hadronize
into a state including the charm meson. This recombination
mechanism can be calculated within perturbative QCD up to
some nonperturbative constants. After using symmetries of
QCD to reduce the number of free parameters to two, we
obtain a good fit to all the data on the asymmetries for
charmed mesons from the E687 and E691 experiments.},
Key = {fds3892}
}
@article{fds3891,
Author = {A. V. Manohar and T. Mehen and D. Pirjol and I. W.
Stewart},
Title = {Reparametrization Invariance for Collinear
Operators},
Journal = {Phys. Lett. B539},
Pages = {59-66},
Year = {2002},
url = {http://arxiv.org/abs/hep-ph/0204229},
Abstract = {We discuss restrictions on operators in the soft-collinear
effective theory (SCET) which follow from the ambiguity in
the decomposition of collinear momenta and the freedom in
the choice of light-like basis vectors n and $\bar{n}$.
Invariance of SCET under small changes in n and/or $\bar{n}$
implies a symmetry of the effective theory that constrains
the form of allowed operators with collinear fields. The
restrictions occur at a given order in the power counting as
well as between different orders. As an example, we present
the complete set of higher order operators that are related
to the collinear quark kinetic term.},
Key = {fds3891}
}
@article{fds3893,
Author = {E. Braaten and Yu Jia and T. Mehen},
Title = {B Production Asymmetries in Perturbative
QCD},
Journal = {Phys. Rev. D66, 034003},
Year = {2002},
url = {http://arxiv.org/abs/hep-ph/0108201},
Abstract = {This paper explores a new mechanism for B production in
which a b quark combines with a light parton from the
hard-scattering process before hadronizing into the B
hadron. This recombination mechanism can be calculated
within perturbative QCD up to a few nonperturbative
constants. Though suppressed at large transverse momentum by
a factor Lambda_QCD m_b/p_t^2 relative to b quark
fragmentation production, it can be important at large
rapidities. A signature for this heavy-quark recombination
mechanism in proton-antiproton colliders is the presence of
rapidity asymmetries in B cross sections. Given reasonable
assumptions about the size of nonperturbative parameters
entering the calculation, we find that the asymmetries are
only significant for rapidities larger than those currently
probed by collider experiments.},
Key = {fds3893}
}
@article{fds3894,
Author = {E. Braaten and H. W. Hammer and T. Mehen},
Title = {Dilute Bose-Einstein Condensate with Large Scattering
Length},
Journal = {Phys. Rev. Lett. 88, 040401},
Year = {2002},
url = {http://arxiv.org/abs/cond-mat/0108380},
Abstract = {We study a dilute Bose gas of atoms whose scattering length
a is large compared to the range of their interaction. We
calculate the energy density of the homogeneous
Bose-Einstein condensate to second order in the low-density
expansion, expressing it in terms of a and a second
parameter Lambda_* that determines the low-energy
observables in the 3-body sector. The second-order
correction to the energy density has a small imaginary part
that reflects the instability due to 3-body recombination.
In the case of a trapped Bose-Einstein condensate with large
negative scattering length, we calculate the coefficient of
the 3-body mean-field term in the energy density in terms of
a and Lambda_*. It can be very large if there is an Efimov
state near threshold.},
Key = {fds3894}
}
@article{fds3897,
Author = {H.W. Hammer and T. Mehen},
Title = {Range Corrections to Doublet S-Wave Neutron-Deuteron
Scattering},
Journal = {Phys. Lett. B},
Volume = {516},
Pages = {353-361},
Year = {2001},
Abstract = {We calculate the range corrections to S-wave
neutron-deuteron scattering in the doublet channel (S=1/2)
to first order in r/a where a is the scattering length and r
the effective range. Ultraviolet divergences appearing at
this order can be absorbed into a redefinition of the
leading order three-body force. The corrections to the
elastic scattering amplitude below the deuteron breakup
threshold are computed. Inclusion of the range corrections
gives good agreement with measured scattering data and
potential model calculations.},
Key = {fds3897}
}
@article{fds3899,
Author = {H.W. Hammer and T. Mehen},
Title = {A Renormalized Equation for the Three-Body System with
Short-Range Interactions},
Journal = {Nucl. Phys. A},
Volume = {690},
Pages = {535-546},
Year = {2001},
Abstract = {We study the three-body system with short-range interactions
characterized by an unnaturally large two-body scattering
length. We show that the off-shell scattering amplitude is
cutoff independent up to power corrections. This allows us
to derive an exact renormalization group equation for the
three-body force. We also obtain a renormalized equation for
the off-shell scattering amplitude. This equation is
invariant under discrete scale transformations. The
periodicity of the spectrum of bound states originally
observed by Efimov is a consequence of this symmetry. The
functional dependence of the three-body scattering length on
the two-body scattering length can be obtained analytically
using the asymptotic solution to the integral equation. An
analogous formula for the three-body recombination
coefficient is also obtained.},
Key = {fds3899}
}
@article{fds3898,
Author = {T. Mehen and M. B. Wise},
Title = {Generalized *-Products, Wilson Lines and the Solution of the
Seiberg-Witten Equations},
Journal = {JHEP},
Volume = {12},
Pages = {8},
Year = {2000},
Abstract = {Higher order terms in the effective action of noncommutative
gauge theories exhibit generalizations of the *-product
(e.g. *' and *-3). These terms do not manifestly respect the
noncommutative gauge invariance of the tree level action. In
U(1) gauge theories, we note that these generalized
*-products occur in the expansion of some quantities that
are invariant under noncommutative gauge transformations,
but contain an infinite number of powers of the
noncommutative gauge field. One example is an open Wilson
line. Another is the expression for a commutative field
strength tensor in terms of the noncommutative gauge field.
Seiberg and Witten derived differential equations that
relate commutative and noncommutative gauge transformations,
gauge fields and field strengths. In the U(1) case we solve
these equations neglecting terms of fourth order in the
gauge field but keeping all orders in the noncommutative
parameter.},
Key = {fds3898}
}
@article{fds3900,
Author = {O. Aharony and J. Gomis and T. Mehen},
Title = {On Theories with Lightlike Noncommutativity},
Journal = {JHEP},
Volume = {9},
Pages = {23},
Year = {2000},
Abstract = {We show that field theories with light-like
noncommutativity, that is with $\theta^{0i}=-\theta^{1i}$,
are unitary quantum theories, and that they can be obtained
as decoupled field theory limits of string theory with
D-branes in a background NS-NS $B$ field. For general
noncommutativity parameters, we show that noncommutative
field theories which are unitary can be obtained as
decoupled field theory limits of string theory, while those
that are not unitary cannot be obtained from string theory
because massive open strings do not decouple. We study the
different theories with light-like noncommutativity which
arise from Type II D-branes. The decoupling limit of the
D4-brane seems to lead to a noncommutative field theory
deformation of the $(2,0)$ SCFT of M5-branes, while the
D5-brane case leads to a noncommutative variation of
``little string theories''. We discuss the DLCQ description
of these theories.},
Key = {fds3900}
}
@article{fds3901,
Author = {J. Gomis and T. Mehen and M. B. Wise},
Title = {Quantum Field Theories with Compact Noncommutative Extra
Dimensions},
Journal = {JHEP},
Volume = {8},
Pages = {29},
Year = {2000},
Abstract = {We study field theories on spaces with additional compact
noncommutative dimensions. As an example, we study \phi^3 on
R^{1,3}\times T^{2}_\theta using perturbation theory. The
infrared divergences in the noncompact theory give rise to
unusual dynamics for the mode of \phi which is constant
along the torus. Correlation functions involving this mode
vanish. Moreover, we show that the spectrum of Kaluza-Klein
excitations can be very different from the analogous
commuting theory. There is an additional contribution to the
Kaluza-Klein mass formula that resembles the contribution of
winding states in string theory. We also consider the effect
of noncommutativity on the four dimensional Kaluza-Klein
excitations of a six dimensional gauge field.},
Key = {fds3901}
}
@article{fds3902,
Author = {J. Gomis and T. Mehen},
Title = {Space-Time Noncommutative Field Theories And
Unitarity},
Journal = {Nucl. Phys. B},
Volume = {591},
Pages = {265-276},
Year = {2000},
Abstract = {We study the perturbative unitarity of noncommutative scalar
field theories. Field theories with space-time
noncommutativity do not have a unitary S-matrix. Field
theories with only space noncommutativity are perturbatively
unitary. This can be understood from string theory, since
space noncommutative field theories describe a low energy
limit of string theory in a background magnetic field. On
the other hand, there is no regime in which space-time
noncommutative field theory is an appropriate description of
string theory. Whenever space-time noncommutative field
theory becomes relevant massive open string states cannot be
neglected.},
Key = {fds3902}
}
@article{fds3903,
Author = {J. Gomis and M. Kleban and T. Mehen and M. Rangamani and S.
Shenker},
Title = {Noncommutative Gauge Dynamics from the String World
Sheet},
Journal = {JHEP},
Volume = {8},
Pages = {11},
Year = {2000},
Abstract = {We show how string theory can be used to reproduce the
one-loop two-point photon amplitude in noncommutative U(1)
gauge theory. Using a simple realization of the gauge theory
in bosonic string theory, we extract from a string cylinder
computation in the decoupling limit the exact one loop field
theory result. The result is obtained entirely from the
region of moduli space where massless open strings dominate.
Our computation indicates that the unusual IR/UV
singularities of noncommutative field theory do not come
from closed string modes in any simple way.},
Key = {fds3903}
}
@article{fds3904,
Author = {S. Fleming and T. Mehen and I. W. Stewart},
Title = {NNLO Corrections to Nucleon-Nucleon Scattering and
Perturbative Pions},
Journal = {Nucl. Phys. A},
Volume = {677},
Pages = {313-366},
Year = {2000},
Abstract = {The 1S0, 3S1, and 3D1 nucleon-nucleon scattering phase
shifts are calculated at next-to-next-to-leading order
(NNLO) in an effective field theory. Predictions for the
1P1, 3P0, 3P1, 3P2, 1D2, 3D2, and 3D3 phase shifts at this
order are also compared with data. The calculations treat
pions perturbatively and include the NNLO contributions from
order $Q_r^3$ and $Q_r^4$ radiation pion graphs. In the 3S1,
3D1, 3P0, and 3P2 channels we find large disagreement with
the Nijmegen partial wave analysis at NNLO. These spin
triplet channels have large corrections from graphs with two
potential pion exchange which do not vanish in the chiral
limit. We compare our results to calculations within the
Weinberg approach, and find that in some spin triplet
channels the summation of potential pion diagrams seems to
be necessary to reproduce the observed phase shifts. In the
spin singlet channels the nonperturbative treatment of
potential pions does not afford a significant improvement
over the perturbative approach.},
Key = {fds3904}
}
@article{fds3905,
Author = {T. Mehen and I. W. Stewart and M.B. Wise},
Title = {Conformal Invariance for Non-Relativistic Field
Theory},
Journal = {Phys. Lett. B},
Volume = {474},
Pages = {145-152},
Year = {2000},
Abstract = {Momentum space Ward identities are derived for the amputated
n-point Green's functions in 3+1 dimensional
non-relativistic conformal field theory. For n=4 and 6 the
implications for scattering amplitudes (i.e. on-shell
amputated Green's functions) are considered. Any scale
invariant 2-to-2 scattering amplitude is also conformally
invariant. However, conformal invariance imposes constraints
on off-shell Green's functions and the three particle
scattering amplitude which are not automatically satisfied
if they are scale invariant. As an explicit example of a
conformally invariant theory we consider non-relativistic
particles in the infinite scattering length
limit.},
Key = {fds3905}
}
@article{fds3906,
Author = {S. Fleming and T. Mehen and I. W. Stewart},
Title = {The NN Scattering $^3S_1-{}^3D_1$ Mixing Angle at
NNLO},
Journal = {Phys. Rev. C},
Volume = {61},
Pages = {044005},
Year = {2000},
Abstract = {The 3S1-3D1 mixing angle for nucleon-nucleon scattering,
epsilon_1, is calculated to next-to-next-to-leading order in
an effective field theory with perturbative pions. Without
pions, the low energy theory fits the observed epsilon_1
well for momenta less than $\sim 50$ MeV. Including pions
perturbatively significantly improves the agreement with
data for momenta up to $\sim 150$ MeV with one less
parameter. Furthermore, for these momenta the accuracy of
our calculation is similar to an effective field theory
calculation in which the pion is treated non-perturbatively.
This gives phenomenological support for a perturbative
treatment of pions in low energy two-nucleon processes. We
explain why it is necessary to perform spin and isospin
traces in d dimensions when regulating divergences with
dimensional regularization in higher partial wave
amplitudes.},
Key = {fds3906}
}
@article{fds3907,
Author = {T. Mehen and I.W. Stewart},
Title = {Nucleon-Nucleon Effective Field Theory at NNLO: Radiation
Pions and $^1S_0$ Phase Shift},
Series = {Proc. Inst. Nucl. Theor. 9},
Booktitle = {Proceedings of the INT Workshop on Nuclear Physics with
Effective Field Theory},
Publisher = {World Scientific},
Editor = {P. Bedaque and M. Savage and R. Seki and U. L. Van
Kolck},
Year = {2000},
Abstract = {Low energy phenomena involving two nucleons can be
successfully described using effective field theory. Because
of the relatively large expansion parameter, it is only at
next-to-next-to-leading order (NNLO) where one can expect to
see agreement with experiment at the few percent level. The
first part of this talk will focus on radiation pion
effects, which first appear at NNLO. The power counting for
radiation pions is simple for center of mass momentum
p~\sqrt{M m_pi}=Q_r, the threshold for pion production. We
explain how graphs calculated with the Q_r power counting
scale for p~m_\pi. The Q_r^3 radiation pion contributions to
nucleon-nucleon scattering are suppressed by inverse powers
of the S-wave scattering lengths. However, we point out that
order Q_r^4 radiation contributions might give a NNLO
contribution for p~m_pi. In the second part of the talk,
results for the potential pion and contact interaction part
of the NNLO 1S0 phase shift are presented. We emphasize the
importance of eliminating spurious poles in the expression
for the amplitude at each order in the perturbative
expansion. Doing this leaves a total of three free
parameters at NNLO. We obtain a good fit to the 1S0 phase
shift.},
Key = {fds3907}
}
@article{fds3909,
Author = {T. Mehen and I. W. Stewart},
Title = {Radiation Pions in Two Nucleon Effective Field
Theory},
Journal = {Nucl. Phys. A},
Volume = {665},
Pages = {164-182},
Year = {2000},
Abstract = {For interactions involving two or more nucleons it is useful
to divide pions into three classes: potential, radiation,
and soft. The momentum threshold for the production of
radiation pions is $Q_r = \sqrt{M_N m_\pi}$. We show that
radiation pions can be included systematically with a power
counting in $Q_r$. The leading order radiation pion graphs
which contribute to NN scattering are evaluated in the PDS
and OS renormalization schemes and are found to give a small
contribution. The power counting for soft pion contributions
is also discussed.},
Key = {fds3909}
}
@article{fds3908,
Author = {T. Mehen and I. W. Stewart and M.B. Wise},
Title = {Wigner Symmetry in the Limit of Large Scattering
Lengths},
Journal = {Phys. Rev. Lett.},
Volume = {83},
Pages = {931-934},
Year = {1999},
Abstract = {We note that in the limit where the NN 1S0 and 3S1
scattering lengths, a^(1S0) and a^(3S1), go to infinity, the
leading terms in the effective field theory for strong NN
interactions are invariant under Wigner's SU(4) spin-isospin
symmetry. This explains why the leading effects of radiation
pions on the S-wave NN scattering amplitudes vanish as
a^(1S0) and a^(3S1) go to infinity. The implications of
Wigner symmetry for NN to NN axion and gamma d to n p are
also considered.},
Key = {fds3908}
}
@article{fds3910,
Author = {T. Mehen},
Title = {Leptoproduction of $J/\Psi$},
Booktitle = {Proceedings of the 29th International Conference on High
Energy Physics (ICHEP 98)},
Publisher = {World Scientific},
Editor = {A. Astbury and D. Axen and J. Robinson},
Year = {1999},
Abstract = {I review the status of the extraction of NRQCD color-octet
$J/\psi$ production matrix elements. Large theoretical
uncertainties in current extractions from hadroproduction
and photoproduction are emphasized. Leptoproduction of
$J/\psi$ is calculated within the NRQCD factorization
formalism. Color-octet contributions dominate the cross
section, allowing for a reliable extraction of $<{\cal
O}_8^{J/\psi}(^1S_0)>$ and $<{\cal O}_8^{J/\psi}(^3P_0)>$. A
comparison with preliminary data from the H1 collaboration
shows that leading order color-octet mechanisms agree with
the measured total cross section for $Q^2 > 4m_c^2$, while
the color-singlet model underpredicts the cross section by a
factor of 5.},
Key = {fds3910}
}
@article{fds3911,
Author = {T. Mehen and I. W. Stewart},
Title = {Renormalization Schemes and the Range of Two Nucleon
Effective Field Theory},
Journal = {Phys. Rev. C},
Volume = {59},
Pages = {2365-2383},
Year = {1999},
Abstract = {The OS and PDS renormalization schemes for the effective
field theory with nucleons and pions are investigated. We
explain in detail how the renormalization is implemented
using local counterterms. Fits to the NN scattering data are
performed in the 1S0 and 3S1 channels for different values
of mu_R. An error analysis indicates that the range of the
theory with perturbative pions is consistent with 500
MeV.},
Key = {fds3911}
}
@article{fds3912,
Author = {T. Mehen and I. W. Stewart},
Title = {A Momentum Subtraction Scheme for Two Nucleon Effective
Field Theory},
Journal = {Phys. Lett. B},
Volume = {445},
Pages = {378-386},
Year = {1999},
Key = {fds3912}
}
@booklet{Fleming98,
Author = {S. Fleming and T. Mehen},
Title = {Photoproduction of h(c)},
Journal = {Physical Review D},
Volume = {5803},
Number = {3},
Pages = {art. no. -- 037503},
Year = {1998},
Month = {August},
Key = {Fleming98}
}
@booklet{Fleming98a,
Author = {S. Fleming and T. Mehen},
Title = {Leptoproduction of J/Psi},
Journal = {Physical Review D},
Volume = {57},
Number = {3},
Pages = {1846 -- 1857},
Year = {1998},
Month = {February},
Key = {Fleming98a}
}
@booklet{Mehen98,
Author = {T. Mehen},
Title = {Summing O(beta(n)(0)alpha(n+1)(s)) corrections to top quark
decays},
Journal = {Physics Letters B},
Volume = {417},
Number = {3-4},
Pages = {353 -- 360},
Year = {1998},
Month = {January},
Key = {Mehen98}
}
@booklet{Mehen97,
Author = {T. Mehen},
Title = {Testing quarkonium production with photoproduced
J/psi+gamma},
Journal = {Physical Review D},
Volume = {55},
Number = {7},
Pages = {4338 -- 4343},
Year = {1997},
Month = {April},
Key = {Mehen97}
}
@booklet{Mehen96,
Author = {T. Mehen},
Title = {Scale setting in top quark decays},
Journal = {Physics Letters B},
Volume = {382},
Number = {3},
Pages = {267 -- 272},
Year = {1996},
Month = {August},
Key = {Mehen96}
}
@booklet{Falk96,
Author = {A. F. Falk and T. Mehen},
Title = {Excited heavy mesons beyond leading order in the heavy quark
expansion},
Journal = {Physical Review D},
Volume = {53},
Number = {1},
Pages = {231 -- 240},
Year = {1996},
Month = {January},
Key = {Falk96}
}
%% Papers Submitted
@article{fds152774,
Author = {Chul Kim and Thomas Mehen},
Title = {Color Octet Scalar Bound States at the LHC},
Journal = {to PRD},
Year = {2008},
url = {http://arXiv.org/abs/0812.0307},
Abstract = {One possible extension of the Standard Model scalar sector
includes SU(2)_L doublet scalars that are color octets
rather than singlets. We focus on models in which the
couplings to fermions are consistent with the principle of
minimal flavor violation (MFV), in which case these color
octet scalars couple most strongly to the third generation
of quarks. When the Yukawa coupling of color octet scalars
to Standard Model fermions is less than unity, these states
can live long enough to bind into color-singlet spin-0
hadrons, which we call octetonia. In this paper, we consider
the phenomenology of octetonia at the Large Hadron Collider
(LHC). Predictions for their production via gluon-gluon
fusion and their two-body decays into Standard Model gauge
bosons, Higgs bosons, and \bar{t}t are presented.},
Key = {fds152774}
}