%% Papers Published @article{fds328273, Author = {Bain, R and Makris, Y and Mehen, T and Dai, L and Leibovich, AK}, Title = {NRQCD Confronts LHCb Data on Quarkonium Production within Jets.}, Journal = {Physical Review Letters}, Volume = {119}, Number = {3}, Pages = {032002}, Year = {2017}, Month = {July}, url = {http://dx.doi.org/10.1103/physrevlett.119.032002}, Abstract = {We analyze the recent LHCb measurement of the distribution of the fraction of the transverse momentum, z(J/ψ), carried by the J/ψ within a jet. LHCb data are compared with analytic calculations using the fragmenting jet function (FJF) formalism for studying J/ψ in jets. Logarithms in the FJFs are resummed using Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution. We also convolve hard QCD partonic cross sections, showered with pythia, with leading order nonrelativistic quantum chromodynamics (NRQCD) fragmentation functions and obtain consistent results. Both approaches use madgraph to calculate the hard process that creates the jet initiating parton. These calculations give reasonable agreement with the z(J/ψ) distribution that was shown to be poorly described by default pythia simulations in the LHCb paper. We compare our predictions for the J/ψ distribution using various extractions of nonperturbative NRQCD long-distance matrix elements (LDMEs) in the literature. NRQCD calculations agree with LHCb data better than default pythia regardless of which fit to the LDMEs is used. LDMEs from fits that focus exclusively on high transverse momentum data from colliders are in good agreement with the LHCb measurement.}, Doi = {10.1103/physrevlett.119.032002}, Key = {fds328273} } @article{fds327375, Author = {Yao, X and Mehen, T and Müller, B}, Title = {Dynamical screening of resonant scattering and thermal nuclear scattering rate in a plasma}, Journal = {Physical Review D}, Volume = {95}, Number = {11}, Year = {2017}, Month = {June}, url = {http://dx.doi.org/10.1103/PhysRevD.95.116002}, Doi = {10.1103/PhysRevD.95.116002}, Key = {fds327375} } @article{fds322008, Author = {Bain, R and Makris, Y and Mehen, T}, Title = {Transverse momentum dependent fragmenting jet functions with applications to quarkonium production}, Journal = {The Journal of High Energy Physics}, Volume = {2016}, Number = {11}, Year = {2016}, Month = {November}, url = {http://dx.doi.org/10.1007/JHEP11(2016)144}, Doi = {10.1007/JHEP11(2016)144}, Key = {fds322008} } @article{fds322009, Author = {Yao, X and Mehen, T and Müller, B}, Title = {An effective field theory approach to the stabilization of 8 Be in a QED plasma}, Journal = {Journal of Physics G: Nuclear and Particle Physics}, Volume = {43}, Number = {7}, Pages = {07LT02-07LT02}, Year = {2016}, Month = {July}, url = {http://dx.doi.org/10.1088/0954-3899/43/7/07LT02}, Doi = {10.1088/0954-3899/43/7/07LT02}, Key = {fds322009} } @article{fds322010, Author = {Bain, R and Dai, L and Hornig, A and Leibovich, AK and Makris, Y and Mehen, T}, Title = {Analytic and Monte Carlo studies of jets with heavy mesons and quarkonia}, Journal = {The Journal of High Energy Physics}, Volume = {2016}, Number = {6}, Year = {2016}, Month = {June}, url = {http://dx.doi.org/10.1007/JHEP06(2016)121}, Doi = {10.1007/JHEP06(2016)121}, Key = {fds322010} } @article{fds322011, Author = {Hornig, A and Makris, Y and Mehen, T}, Title = {Jet shapes in dijet events at the LHC in SCET}, Journal = {The Journal of High Energy Physics}, Volume = {2016}, Number = {4}, Pages = {1-41}, Year = {2016}, Month = {April}, url = {http://dx.doi.org/10.1007/JHEP04(2016)097}, Doi = {10.1007/JHEP04(2016)097}, Key = {fds322011} } @article{fds287615, Author = {Mehen, T}, Title = {Hadronic loops versus factorization in effective field theory calculations of}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {92}, Number = {3}, Year = {2015}, Month = {August}, ISSN = {1550-7998}, url = {http://dx.doi.org/10.1103/PhysRevD.92.034019}, Doi = {10.1103/PhysRevD.92.034019}, Key = {fds287615} } @article{fds322012, Author = {Mehen, T}, Title = {New tests of NRQCD from Quarkonia within jets}, Journal = {PoS - Proceedings of Science}, Volume = {26-30-May-2015}, Year = {2015}, Month = {January}, Abstract = {I review the current status of quarkonium production theory based on the non-relativistic QCD factorization formalism (NRQCD). While this theory describes much of the world's data on J=y and ¡ production, there are still outstanding problems, most notably the polarization of quarkonia at large pT in hadron colliders. In this talk we will present new tests of NRQCD involving the distribution of quarkonia within jets. The distribution of hadrons within jets is determined by nonperturbative functions called fragmenting jet functions (FJFs). FJFs are convolutions of fragmentation functions, evolved to the jet energy scale, with perturbatively calculable matching coefficients. I show how the FJFs for quarkonia can be calculated in NRQCD in terms of a few NRQCD long-distance matrix elements (LDME), so the dependence of the cross section on the energy fraction of the heavy quarkonium, z, is sensitive to the underlying production mechanism, and therefore provides a new test of NRQCD. The jet energy and z dependence of the cross section can be used to perform an independent extraction of NRQCD LDME. Finally, I describe ongoing work building on this result. This includes comparison of analytic resummed calculations with Monte Carlo simulations for two-jet events in e + e - collisions with B mesons, and three-jet events with J=y, as well as the definition of boost invariant jet substructure variables and calculation of a boost invariant soft function that are necessary for analytic calculations of jet cross sections at the Large Hadron Collider. QCD.}, Key = {fds322012} } @article{fds287614, Author = {Baumgart, M and Leibovich, AK and Mehen, T and Rothstein, IZ}, Title = {Probing quarkonium production mechanisms with jet substructure}, Journal = {The Journal of High Energy Physics}, Volume = {2014}, Number = {11}, Year = {2014}, Month = {November}, url = {http://arxiv.org/abs/arXiv:1406.2295}, Doi = {10.1007/JHEP11(2014)003}, Key = {fds287614} } @article{fds287618, Author = {Kim, C and Idilbi, A and Mehen, T and Yoon, YW}, Title = {Production of stoponium at the LHC}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {89}, Number = {7}, Year = {2014}, Month = {April}, ISSN = {1550-7998}, url = {http://arxiv.org/abs/arXiv:1401.1284}, Doi = {10.1103/PhysRevD.89.075010}, Key = {fds287618} } @article{fds221123, Author = {Thomas Mehen and Joshua W. Powell}, Title = {Line shapes in Υ(5S)→B^{(∗)}B^{(∗)}π with Z(10610) and Z(10650) using effective field theory}, Journal = {Phys. Rev. D88:034017}, Year = {2013}, url = {http://arxiv.org/abs/1306.5459}, Key = {fds221123} } @article{fds287621, Author = {Mehen, T and Powell, JW}, Title = {Line shapes in Υ(5S)→B(^{*})B^{̄}(^{*})π with Z(10610) and Z(10650) using effective field theory}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {88}, Number = {3}, Year = {2013}, ISSN = {1550-7998}, url = {http://dx.doi.org/10.1103/PhysRevD.88.034017}, Abstract = {The Belle Collaboration recently discovered two resonances, Z b(10610) and Zb(10650) - denoted Zb and Zb′ - in the decays Υ(5S)→Υ(nS)π+π - for n=1, 2, or 3, and Υ(5S)→hb(mP) π+π- for m=1 or 2. These resonances lie very close to the B*B̄ and B*B̄* thresholds, respectively. A recent Belle analysis of the three-body decays Υ(5S)→[B(*)B̄( *)]â̂π± gives further evidence for the existence of these states. In this paper we analyze this decay using an effective theory of B mesons interacting via strong short-range interactions. Some parameters in this theory are constrained using existing data on Υ(5S)→B(*)B̄( *) decays, which requires the inclusion of heavy quark spin symmetry violating operators. We then calculate the differential distribution for Υ(5S)→B(*)B̄(*) π as a function of the invariant mass of the B(*)B ̄(*) pair, obtaining qualitative agreement with experimental data. We also calculate angular distributions in the decay Υ(5S)→Zb(′)π which are sensitive to the molecular character of the Zb(′). © 2013 American Physical Society.}, Doi = {10.1103/PhysRevD.88.034017}, Key = {fds287621} } @article{fds287622, Author = {Fleming, S and Leibovich, AK and Mehen, T and Rothstein, IZ}, Title = {Anomalous dimensions of the double parton fragmentation functions}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {87}, Number = {7}, Year = {2013}, ISSN = {1550-7998}, url = {http://arxiv.org/abs/arXiv:1301.3822}, Abstract = {Double parton fragmentation is a process in which a pair of partons produced in the short-distance process hadronize into the final state hadron. This process is important for quarkonium production when the transverse momentum is much greater than the quark mass. Resummation of logarithms of the ratio of these two scales requires the evolution equations for double parton fragmentation functions (DPFF). In this paper we complete the one-loop evaluation of the anomalous dimensions for the DPFF. We also consider possible mixing between the DPFF and single parton power suppressed gluon fragmentation and show that such effects are subleading. © 2013 American Physical Society.}, Doi = {10.1103/PhysRevD.87.074022}, Key = {fds287622} } @article{fds287643, Author = {Mehen, T and Yang, D-L}, Title = {The role of charmed meson loops in charmonium decays}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {85}, Number = {1}, Year = {2012}, ISSN = {1550-7998}, url = {http://dx.doi.org/10.1103/PhysRevD.85.014002}, Abstract = {We investigate the effect of intermediate charmed meson loops on the M1 radiative decays J/ψ→η cγ and ψ ′→ηc(′)γ as well as the isospin [SU(3)] violating hadronic decays ψ ′→J/ψπ0(η) using heavy hadron chiral perturbation theory. The calculations include tree level as well as one loop diagrams and are compared to the latest data from CLEO and BES-III. Our fit constrains the couplings of 1S and 2S charmonium multiplets to charmed mesons, denoted g 2 and g2′, respectively. We find that there are two sets of solutions for g 2 and g2′. One set, which agrees with previous values of the product g 2g2′ extracted from analyses that consider only loop contributions to ψ ′→ J/ψπ0(η), can only fit data on radiative decays with fine-tuned cancellations between tree level diagrams and loops in that process. The other solution for g 2 and g2′ leads to couplings that are smaller by a factor of 2.3. In this case tree level and loop contributions are of comparable size and the numerical values of the tree level contributions to radiative decays are consistent with estimates based on the quark model as well as nonrelativistic QCD. This result shows that tree level heavy hadron chiral perturbation theory couplings are as important as the one loop graphs with charmed mesons in these charmonium decays. The couplings g 2 and g2′ are also important for the calculations of the decays of charmed meson bound states, such as the X(3872), to conventional charmonia. © 2012 American Physical Society.}, Doi = {10.1103/PhysRevD.85.014002}, Key = {fds287643} } @article{fds287645, Author = {Fleming, S and Mehen, T}, Title = {Decay of the X(3872) into χ_{cJ}and the operator product expansion in effective field theory}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {85}, Number = {1}, Year = {2012}, ISSN = {1550-7998}, url = {http://dx.doi.org/10.1103/PhysRevD.85.014016}, Abstract = {We consider a low-energy effective theory for the X(3872) (XEFT) that can be used to systematically analyze the decay and production of the X(3872) meson, assuming that it is a weakly bound state of charmed mesons. In a previous paper, we calculated the decays of X(3872) into χ cJ plus pions using a two-step procedure in which Heavy Hadron Chiral Perturbation Theory (HHχPT) amplitudes are matched onto XEFT operators and then X(3872) decay rates are calculated using these operators. The procedure leads to IR divergences in the three-body decay X(3872)→χ cJππ when virtual D mesons can go on shell in tree level HHχPT diagrams. In previous work, we regulated these IR divergences with the D *0 width. In this work, we carefully analyze X(3872)→χ cJπ0 and X(3872)→χ cJππ using the operator product expansion in XEFT. Forward scattering amplitudes in HHχPT are matched onto local operators in XEFT, the imaginary parts of which are responsible for the decay of the X(3872). Here we show that the IR divergences are regulated by the binding momentum of the X(3872) rather than the width of the D *0 meson. In the operator product expansion, these IR divergences cancel in the calculation of the matching coefficients so the correct predictions for the X(3872)→χ c1ππ do not receive enhancements due to the width of the D *0. We give updated predictions for the decay X(3872)→χ c1ππ at leading order in XEFT. © 2012 American Physical Society.}, Doi = {10.1103/PhysRevD.85.014016}, Key = {fds287645} } @article{fds287646, Author = {Fleming, S and Leibovich, AK and Mehen, T and Rothstein, IZ}, Title = {Systematics of quarkonium production at the LHC and double parton fragmentation}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {86}, Number = {9}, Year = {2012}, ISSN = {1550-7998}, url = {http://arxiv.org/abs/1301.3822}, Abstract = {In this paper, we discuss the systematics of quarkonium production at the LHC. In particular, we focus on the necessity to sum logs of the form log(Q/p ≥) and log(p ≥/m Q). We show that the former contributions are power suppressed, while the latter, whose contribution in fragmentation is well known, also arise in the short distance (i.e., nonfragmentation) production mechanisms. Though these contributions are suppressed by powers of m Q/p ≥, they can be enhanced by inverse powers of v, the relative velocity between heavy quarks in the quarkonium. In the limit p ≥m Q, short-distance production can be thought of as the fragmentation of a pair of partons (i.e., the heavy quark and antiquark) into the final state quarkonium. We derive an all-order factorization theorem for this process in terms of double parton fragmentation functions and calculate the one-loop anomalous dimension matrix for the double parton fragmentation functions. © 2012 American Physical Society.}, Doi = {10.1103/PhysRevD.86.094012}, Key = {fds287646} } @article{fds287647, Author = {Mehen, T and Yang, D-L}, Title = {On the Role of Charmed Meson Loops in Charmonium Decays}, Journal = {Phys.Rev. D85:014002}, Year = {2012}, url = {http://arxiv.org/abs/1111.3884}, Key = {fds287647} } @article{fds287648, Author = {Fleming, S and Mehen, T}, Title = {The decay of the X(3872) into &chicJ and the Operator Product Expansion in XEFT}, Journal = {Phys.Rev. D85:014016}, Year = {2012}, url = {http://arxiv.org/abs/1110.0265}, Key = {fds287648} } @article{fds287644, Author = {Mehen, T and Powell, JW}, Title = {Heavy quark symmetry predictions for weakly bound B-meson molecules}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {84}, Number = {11}, Year = {2011}, ISSN = {1550-7998}, url = {http://arxiv.org/abs/1109.3479}, Abstract = {Recently the Belle collaboration discovered two resonances, Z b(10610) and Z b(10650), that lie very close to the BB ̄* and B *B ̄* thresholds, respectively. It is natural to suppose that these are molecular states of bottom and antibottom mesons. Under this assumption, we introduce an effective field theory for the Z b(10610) and Z b(10650), as well as similar unobserved states that are expected on the basis of heavy quark spin symmetry. The molecules are assumed to arise from short-range interactions that respect heavy quark spin symmetry. We use the theory to calculate line shapes in the vicinity of B( *)B ̄(*) thresholds as well as two-body decay rates of the new bottom meson bound states. We derive new heavy quark spin symmetry predictions for the parameters appearing in the line shapes as well as the total and partial widths of the states. © 2011 American Physical Society.}, Doi = {10.1103/PhysRevD.84.114013}, Key = {fds287644} } @article{fds287649, Author = {Mehen, T and Springer, R}, Title = {Radiative Decays of X(3872) &rarr &psi(2S) &gamma and &psi(4040) &rarr X(3872) &gamma in Effective Field Theory}, Journal = {Phys.Rev.D83:094009}, Volume = {83}, Number = {9}, Year = {2011}, ISSN = {1550-7998}, url = {http://arxiv.org/abs/1101.5175}, Abstract = {Heavy hadron chiral perturbation theory (HHÏ‡PT) and XEFT are applied to the decays X(3872)â†’Ïˆ(2S)Î³ and Ïˆ(4040)â†’X(3872)Î³ under the assumption that the X(3872) is a molecular bound state of neutral charm mesons. In these decays the emitted photon energies are 181MeV and 165MeV, respectively, so HHÏ‡PT can be used to calculate the underlying D0D Ì„0*+DÌ„0D0 *â†’Ïˆ(2S)Î³ or Ïˆ(4040)â†’(D0D Ì„0*+DÌ„0D0*) Î³ transition. These amplitudes are matched onto XEFT to obtain decay rates. The decays receive contributions from both long-distance and short-distance processes. We study the polarization of the Ïˆ(2S) in the decay X(3872)â†’Ïˆ(2S)Î³ and the angular distribution of X(3872) in the decay Ïˆ(4040)â†’X(3872)Î³ and find they can be used to differentiate between different decay mechanisms as well as discriminate between 2-+ and 1++ quantum number assignments of the X(3872). Â© 2011 American Physical Society.}, Doi = {10.1103/PhysRevD.83.094009}, Key = {fds287649} } @article{fds305720, Author = {Mehen, T and Springer, R}, Title = {Radiative decays X(3872)→ψ(2S)γ and ψ(4040)→X(3872) γ in effective field theory}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {83}, Number = {9}, Year = {2011}, ISSN = {1550-7998}, url = {http://dx.doi.org/10.1103/PhysRevD.83.094009}, Abstract = {Heavy hadron chiral perturbation theory (HHχPT) and XEFT are applied to the decays X(3872)→ψ(2S)γ and ψ(4040)→X(3872)γ under the assumption that the X(3872) is a molecular bound state of neutral charm mesons. In these decays the emitted photon energies are 181MeV and 165MeV, respectively, so HHχPT can be used to calculate the underlying D0D ̄0*+D̄0D0 *→ψ(2S)γ or ψ(4040)→(D0D ̄0*+D̄0D0*) γ transition. These amplitudes are matched onto XEFT to obtain decay rates. The decays receive contributions from both long-distance and short-distance processes. We study the polarization of the ψ(2S) in the decay X(3872)→ψ(2S)γ and the angular distribution of X(3872) in the decay ψ(4040)→X(3872)γ and find they can be used to differentiate between different decay mechanisms as well as discriminate between 2-+ and 1++ quantum number assignments of the X(3872). © 2011 American Physical Society.}, Doi = {10.1103/PhysRevD.83.094009}, Key = {fds305720} } @article{fds287650, Author = {Idilbi, A and Kim, C and Mehen, T}, Title = {Pair production of color-octet scalars at the LHC}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {82}, Number = {7}, Year = {2010}, ISSN = {1550-7998}, url = {http://hdl.handle.net/10161/4280 Duke open access}, Abstract = {Heavy colored scalar particles, which exist in many models of new physics, can be pair produced at the LHC via gluon-gluon fusion and possibly form quarkoniumlike bound states. If the scalars are also charged under the electroweak gauge group, these bound states can then decay into electroweak bosons. This yields a resonant cross section for final states such as γγ that can exceed standard model backgrounds. This paper studies this process in the Manohar-Wise model of color-octet scalars (COS). Important threshold logarithms and final state Coulomb-like QCD interactions are resummed using effective field theory. We compute the resummed cross section for gluon-gluon fusion to COS pairs at the LHC as well as the resonant cross section for octetonium decaying to γγ. The latter cross section exceeds the standard model diphoton cross section when the COS mass is less than 500 (350) GeV for √s=14(7)TeV. Nonobservation of resonances below these energies can significantly improve existing bounds on COS masses. © 2010 The American Physical Society.}, Doi = {10.1103/PhysRevD.82.075017}, Key = {fds287650} } @article{fds287651, Author = {Braaten, E and Hammer, H-W and Mehen, T}, Title = {Scattering of an ultrasoft pion and the X(3872)}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {82}, Number = {3}, Year = {2010}, ISSN = {1550-7998}, url = {http://hdl.handle.net/10161/4278 Duke open access}, Abstract = {The identification of the X(3872) as a loosely-bound charm-meson molecule allows it to be described by an effective field theory, called XEFT, for the D*D̄, DD̄*, and DD̄π sector of QCD at energies small compared to the pion mass. We point out that this effective field theory can be extended to the sector that includes an additional pion and used to calculate cross sections for the scattering of a pion and the X(3872). If the collision energy is much smaller than the pion mass, the cross sections are completely calculable at leading order in terms of the masses and widths of the charm mesons, pion masses, and the binding energy of the X(3872). We carry out an explicit calculation of the cross section for the breakup of the X(3872) into D*+D̄*0 by the scattering of a very low energy π+. ©2010 The American Physical Society.}, Doi = {10.1103/PhysRevD.82.034018}, Key = {fds287651} } @article{fds287652, Author = {Idilbi, A and Kim, C and Mehen, T}, Title = {Factorization and resummation for single color-octet scalar production at the LHC}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {79}, Number = {11}, Year = {2009}, ISSN = {1550-7998}, url = {http://arXiv.org/abs/0903.3668}, Abstract = {Heavy colored scalar particles appear in a variety of new physics (NP) models and could be produced at the Large Hadron Collider. Knowing the total production cross section is important for searching for these states and establishing bounds on their masses and couplings. Using soft-collinear effective theory, we derive a factorization theorem for the process pp→SX, where S is a color-octet scalar, that is applicable to any NP model provided the dominant production mechanism is gluon-gluon fusion. The factorized result for the inclusive cross section is similar to that for the standard model Higgs production; however, differences arise due to color exchange between initial and final states. We provide formulas for the total cross section with large (partonic) threshold logarithms resummed to next-to-leading logarithm accuracy. The resulting K factors are similar to those found in Higgs production. We apply our formalism to the Manohar-Wise model and find that the next-to-leading logarithm cross section is roughly 2 times (3 times) as large as the leading order cross section for a color-octet scalar of mass of 500 GeV (3 TeV). A similar enhancement should appear in any NP model with color-octet scalars. © 2009 The American Physical Society.}, Doi = {10.1103/PhysRevD.79.114016}, Key = {fds287652} } @article{fds287653, Author = {Kim, C and Mehen, T}, Title = {Color octet scalar bound states at the LHC}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {79}, Number = {3}, Year = {2009}, ISSN = {1550-7998}, url = {http://arXiv.org/abs/0903.3668}, 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, 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. Predictions for their production via gluon-gluon fusion and their two-body decays into standard model gauge bosons, Higgs bosons, and t̄t are presented. © 2009 The American Physical Society.}, Doi = {10.1103/PhysRevD.79.035011}, Key = {fds287653} } @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{fds287639, Author = {Mehen, T}, Title = {Nonrelativistic conformal field theory and trapped atoms: Virial theorems and the state-operator correspondence in three dimensions}, Journal = {Physical Review A - Atomic, Molecular, and Optical Physics}, Volume = {78}, Number = {1}, Year = {2008}, ISSN = {1050-2947}, url = {http://dx.doi.org/10.1103/PhysRevA.78.013614}, 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 nonrelativistic 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 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. © 2008 The American Physical Society.}, Doi = {10.1103/PhysRevA.78.013614}, Key = {fds287639} } @article{fds287654, Author = {Fleming, S and Mehen, T}, Title = {Hadronic decays of the X(3872) to χcJ in effective field theory}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {78}, Number = {9}, Year = {2008}, ISSN = {1550-7998}, 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 (HHχPT) amplitudes for D0D̄ *0→χcJ(π0,ππ) 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 HHχPT 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 χc1π0π0, with a branching fraction just below that for the decay to χc1π0. Decays to all other final states with two pions are highly suppressed. © 2008 The American Physical Society.}, Doi = {10.1103/PhysRevD.78.094019}, Key = {fds287654} } @article{fds287655, Author = {Kim, C and Leibovich, AK and Mehen, T}, Title = {Nonperturbative charming penguin contributions to isospin asymmetries in radiative B decays}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {78}, Number = {5}, Year = {2008}, ISSN = {1550-7998}, url = {http://arXiv.org/abs/0805.1735}, Abstract = {Recent experimental data on the radiative decays B→Vγ, where V is a light vector meson, find small isospin violation in B→K*γ while isospin asymmetries in B→ργ 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/mb), also including O(vαs) 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→Vγ modes. We also consider the effect of the NPCP on the branching ratio and CP asymmetries in B±→ V±γ. © 2008 The American Physical Society.}, Doi = {10.1103/PhysRevD.78.054024}, Key = {fds287655} } @article{fds287617, Author = {Mehen, T}, Title = {Heavy quark-diquark symmetry and &ChiPT for doubly heavy baryons}, Journal = {Chiral Dynamics 2006 - Proceedings of the 5th International Workshop on Chiral Dynamics, Theory and Experiment, CD 2006}, Pages = {299-301}, Year = {2007}, Month = {December}, Abstract = {A chiral Lagrangian incorporating heavy quark-diquark symmetry is used to calculate doubly charm baryon electromagnetic decays and chiral corrections to doubly heavy baryon masses. Quenched and partially quenched versions of the theory allow one to derive chiral extrapolation formulae for lattice QCD simulations of doubly heavy baryons.}, Key = {fds287617} } @article{fds287656, Author = {Fleming, S and Kusunoki, M and Mehen, T and Kolck, UV}, Title = {Pion interactions in the X(3872)}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {76}, Number = {3}, Year = {2007}, ISSN = {1550-7998}, 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 D0D̄*0 and D*0D̄0. Since the hyperfine splitting of the D0 and D*0 is only 7 MeV greater than the neutral pion mass, pions can be produced near threshold and are nonrelativistic. We show that pion exchange can be treated in perturbation theory and calculate the next-to-leading-order correction to the partial decay width Γ[X→D0D̄0π0]. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevD.76.034006}, Key = {fds287656} } @article{fds287657, Author = {Idilbi, A and Mehen, T}, Title = {Equivalence of soft and zero-bin subtractions at two loops}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {76}, Number = {9}, Year = {2007}, ISSN = {1550-7998}, url = {http://arXiv.org/abs/0707.1101}, Abstract = {Calculations of collinear correlation functions in perturbative QCD and soft-collinear effective theory 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 λ, where λ is the soft-collinear effective theory 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 demonstrate the equivalence, which can be used to give a nonperturbative definition of the zero-bin subtraction at lowest order in λ. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevD.76.094015}, Key = {fds287657} } @article{fds287658, Author = {Idilbi, A and Mehen, T}, Title = {On the equivalence of soft and zero-bin subtractions}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {75}, Number = {11}, Year = {2007}, ISSN = {1550-7998}, 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 xB→1 as examples. We explain how the zero-bin subtractions in SCET are required to reproduce the well-established factorization theorem for DIS as xB→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. © 2007 The American Physical Society.}, Doi = {10.1103/PhysRevD.75.114017}, Key = {fds287658} } @article{fds287616, Author = {Leibovich, A and Fleming, S and Mehen, T}, Title = {J/φ photoproduction at the endpoint}, Journal = {Annual Meeting of the Division of Particles and Fields of the American Physical Society, DPF 2006, and the Annual Fall Meeting of the Japan Particle Physics Community}, Year = {2006}, Month = {January}, Key = {fds287616} } @article{fds287619, Author = {Fleming, S and Leibovich, AK and Mehen, T}, Title = {J/Ψ photo-production at large z in soft collinear effective theory}, Journal = {Proceedings of the Ringberg Workshop on New Trends in HERA Physics 2005}, Pages = {239-250}, Year = {2006}, Month = {January}, url = {http://arxiv.org/abs/hep-ph/0512194}, Abstract = {One of the outstanding problems in J/Ψ physics is a systematic understanding of the differential photo-production cross section dσ/dz(γ+p → J/Ψ + X), where z = E Ψ ,/E gamma; / in the proton rest frame. The theoretical prediction based on the nonrelativistic 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 photoproduction 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. Copyright © 2006 by World Scientific Publishing Co. Pte. Ltd.}, Key = {fds287619} } @article{fds287620, Author = {Mehen, T}, Title = {Heavy quark-diquark symmetry and X PT for Doubly Heavy Baryons}, Journal = {Annual Meeting of the Division of Particles and Fields of the American Physical Society, DPF 2006, and the Annual Fall Meeting of the Japan Particle Physics Community}, Pages = {299-301}, Year = {2006}, Month = {January}, Abstract = {A chiral Lagrangian incorporating heavy quark-diquark symmetry is used to calculate doubly charm baryon electromagnetic decays and chiral corrections to doubly heavy baryon masses. Quenched and partially quenched versions of the theory allow one to derive chiral extrapolation formulae for lattice QCD simulations of doubly heavy baryons.}, Key = {fds287620} } @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{fds287637, Author = {Hu, J and Mehen, T}, Title = {Chiral Lagrangian with heavy quark-diquark symmetry}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {73}, Number = {5}, Year = {2006}, ISSN = {1550-7998}, 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/mQ) symmetry violating operators. The theory is used to predict the electromagnetic decay width of the J=32 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. © 2006 The American Physical Society.}, Doi = {10.1103/PhysRevD.73.054003}, Key = {fds287637} } @article{fds287638, Author = {Fleming, S and Mehen, T}, Title = {Doubly heavy baryons, heavy quark-diquark symmetry, and nonrelativistic QCD}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {73}, Number = {3}, Year = {2006}, ISSN = {1550-7998}, url = {http://dx.doi.org/10.1103/PhysRevD.73.034502}, 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 nonrelativistic 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 QQ̄ and QQ sectors of pNRQCD and give a correct derivation of the O(1/mQ) prediction for the hyperfine splitting of doubly heavy baryons. © 2006 The American Physical Society.}, Doi = {10.1103/PhysRevD.73.034502}, Key = {fds287638} } @article{fds287661, Author = {Fleming, S and Leibovich, AK and Mehen, T}, Title = {Resummation of large endpoint corrections to color-octet J/ψ photoproduction}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {74}, Number = {11}, Year = {2006}, ISSN = {1550-7998}, url = {http://arxiv.org/abs/hep-ph/0607121}, Abstract = {An unresolved problem in J/ψ phenomenology is a systematic understanding of the differential photoproduction cross section, dσ/dz[γ+p→J/ψ+X], where z=Eψ/Eγ in the proton rest frame. In the nonrelativistic 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/ψ 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 dσ/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. © 2006 The American Physical Society.}, Doi = {10.1103/PhysRevD.74.114004}, Key = {fds287661} } @article{fds287662, Author = {Mehen, T and Tiburzi, BC}, Title = {Doubly heavy baryons and quark-diquark symmetry in quenched and partially quenched chiral perturbation theory}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {74}, Number = {5}, Year = {2006}, ISSN = {1550-7998}, 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 formulas for the chiral extrapolation of masses and hyperfine splittings of double 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 formulas for the doubly heavy baryon electromagnetic transition moments are also determined for the partially quenched theory. © 2006 The American Physical Society.}, Doi = {10.1103/PhysRevD.74.054505}, Key = {fds287662} } @article{fds287668, Author = {Mehen, T and Springer, RP}, Title = {Even- and Odd-Parity Charmed Meson Masses in Heavy Hadron Chiral Perturbation Theory}, Journal = {Phys Rev D}, Volume = {72}, Number = {034006}, Pages = {1-12}, Year = {2005}, Month = {March}, ISSN = {1550-7998}, url = {http://arxiv.org/abs/hep-ph/0503134}, Abstract = {We derive mass formulas for the ground state, JP=0- and 1-, and first excited even-parity, JP=0+ and 1+, charmed mesons including one-loop chiral corrections and O(1/mc) 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 observed equality of the hyperfine splittings of ground state and excited doublets. Â© 2005 The American Physical Society.}, Doi = {10.1103/PhysRevD.72.034006}, Key = {fds287668} } @article{fds287669, Author = {Mehen, T}, Title = {Excited D_{s}(and pentaquarks) in chiral perturbation theory}, Journal = {Acta Physica Polonica, Series B.}, Volume = {36}, Number = {7}, Pages = {2341-2350}, Year = {2005}, ISSN = {0587-4254}, 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 10̄ representation of SU(3) which can be used to constrain the angular momentum and parity quantum numbers of these states.}, Key = {fds287669} } @article{fds287670, Author = {Mehen, T and Tiburzi, BC}, Title = {Quarks with twisted boundary conditions in the epsilon regime}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {72}, Number = {1}, Pages = {1-9}, Year = {2005}, ISSN = {1550-7998}, 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)LxSU(2)R chiral theory with nondegenerate quarks and the SU(3)LxSU(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. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevD.72.014501}, Key = {fds287670} } @article{fds305719, Author = {Mehen, T and Springer, RP}, Title = {Even- and odd-parity charmed meson masses in heavy hadron chiral perturbation theory}, Journal = {Physical Review D - Particles, Fields, Gravitation, and Cosmology}, Volume = {72}, Number = {3}, Pages = {1-12}, Year = {2005}, ISSN = {1550-7998}, url = {http://dx.doi.org/10.1103/PhysRevD.72.034006}, Abstract = {We derive mass formulas for the ground state, JP=0- and 1-, and first excited even-parity, JP=0+ and 1+, charmed mesons including one-loop chiral corrections and O(1/mc) 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 observed equality of the hyperfine splittings of ground state and excited doublets. © 2005 The American Physical Society.}, Doi = {10.1103/PhysRevD.72.034006}, Key = {fds305719} } @article{fds287613, Author = {Mehen, T and Springer, RP}, Title = {Heavy-quark symmetry and the electromagnetic decays of excited charmed strange mesons}, Journal = {Physical Review D: Particles, Fields, Gravitation and Cosmology}, Volume = {70}, Number = {7}, Pages = {074014-1-074014-12}, Year = {2004}, Month = {January}, ISSN = {0556-2821}, url = {http://dx.doi.org/10.1103/PhysRevD.70.074014}, Abstract = {Heavy-hadron chiral perturbation theory (HH < inf > χ < /inf > PT) is applied to the decays of the even-parity charmed strange mesons, D < inf > s0 < /inf > (2317) and D < inf > s1 < /inf > (2460). Heavy-quark spin-symmetry predicts the branching fractions for the three electromagnetic decays of these states to the ground states D < inf > s < /inf > and D < inf > s < /inf > * 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 < inf > χ < /inf > PT Lagrangian can naturally account for this discrepancy. Finally the proposal that the D < inf > s0 < /inf > (2317) (D < inf > s1 < /inf > (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.}, Doi = {10.1103/PhysRevD.70.074014}, Key = {fds287613} } @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{fds287612, Author = {Braaten, E and Kusunoki, M and Jia, Y and Mehen, T}, Title = {Λ<inf>c</inf><sup>+</sup>/Λ<inf>c</inf><sup>-</sup> asymmetry in hadroproduction from heavy-quark recombination}, Journal = {Physical Review D: Particles, Fields, Gravitation and Cosmology}, Volume = {70}, Number = {5}, Pages = {054021-1-054021-5}, Year = {2004}, ISSN = {0556-2821}, url = {http://dx.doi.org/10.1103/PhysRevD.70.054021}, 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 Λ<inf>c</inf><sup>+</sup>/Λ<inf>c</inf> <sup>-</sup> asymmetries measured in πN pN collisions.}, Doi = {10.1103/PhysRevD.70.054021}, Key = {fds287612} } @article{fds287635, Author = {Braaten, E and Kusunoki, M and Jia, Y and Mehen, T}, Title = {Λ_{c}^{+}/Λ_{c}^{-}asymmetry in hadroproduction from heavy-quark recombination}, Journal = {Physical Review D - Particles, Fields, Gravitation and Cosmology}, Volume = {70}, Number = {5}, Pages = {054021-1-054021-5}, Year = {2004}, url = {http://dx.doi.org/10.1103/PhysRevD.70.054021}, 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 Λc+/Λc- asymmetries measured in πN pN collisions.}, Doi = {10.1103/PhysRevD.70.054021}, Key = {fds287635} } @article{fds287663, Author = {Mehen, T}, Title = {Charm production asymmetries from heavy-quark recombination}, Journal = {Journal of Physics G: Nuclear and Particle Physics}, Volume = {30}, Number = {1}, Pages = {S295-S304}, Year = {2004}, 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 ΛC asymmetries with a minimal set of universal nonperturbative parameters.}, Doi = {10.1088/0954-3899/30/1/035}, Key = {fds287663} } @article{fds287664, Author = {Mehen, T}, Title = {Recent developments in heavy quark and quarkonium production}, Journal = {Acta Physica Polonica, Series B.}, Volume = {35}, Number = {1}, Pages = {121-129}, Year = {2004}, ISSN = {0587-4254}, url = {http://arxiv.org/abs/hep-ph/0312239}, Abstract = {Recent measurements of J/ψ 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/ψ 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/ψcc̄ 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 = {fds287664} } @article{fds287665, Author = {Braaten, E and Kusunoki, M and Jia, Y and Mehen, T}, 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 = {fds287665} } @article{fds287666, Author = {Mehen, T and Springer, RP}, Title = {Heavy-quark symmetry and the electromagnetic decays of excited charmed strange mesons}, Journal = {Physical Review D - Particles, Fields, Gravitation and Cosmology}, Volume = {70}, Number = {7}, Pages = {074014-1-074014-12}, Year = {2004}, url = {http://dx.doi.org/10.1103/PhysRevD.70.074014}, Abstract = {Heavy-hadron chiral perturbation theory (HHχPT) is applied to the decays of the even-parity charmed strange mesons, Ds0(2317) and Ds1(2460). Heavy-quark spin-symmetry predicts the branching fractions for the three electromagnetic decays of these states to the ground states Ds and Ds* 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 HHχPT Lagrangian can naturally account for this discrepancy. Finally the proposal that the Ds0(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.}, Doi = {10.1103/PhysRevD.70.074014}, Key = {fds287666} } @article{fds287667, Author = {Mehen, T and Schat, C}, Title = {Determining pentaquark quantum numbers from strong decays}, Journal = {Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics}, Volume = {588}, Number = {1-2}, Pages = {67-73}, Year = {2004}, url = {http://arxiv.org/abs/hep-ph/0401107}, Abstract = {Assuming that the recently observed Θ+ and Ξ- 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 JΠ=12±,32± and calculate ratios of partial widths. The branching ratios of exotic cascades can be used to discriminate between even and odd parity pentaquarks. © 2004 Published by Elsevier B.V.}, Doi = {10.1016/j.physletb.2004.03.039}, Key = {fds287667} } @article{fds287633, Author = {Kaiser, R and Manohar, AV and Mehen, T}, Title = {Isospin violation in e^{+}e^{-}→ BB̄}, Journal = {Physical Review Letters}, Volume = {90}, Number = {14}, Pages = {142001/1-142001/4}, Year = {2003}, url = {http://arxiv.org/abs/hep-ph/0208194}, Abstract = {An overview is given of the computation of R+/0. The result depends on two parameters: the Β*Βπ coupling and δc, which represents the isospin violating part of the Y(4S) coupling to Β̄Β states.}, Key = {fds287633} } @article{fds287671, Author = {Fleming, S and Leibovich, AK and Mehen, T}, Title = {Resumming the color-octet contribution to e^{+}e-→J/ψ+X}, Journal = {Physical Review D: Particles, Fields, Gravitation and Cosmology}, Volume = {68}, Number = {9}, Year = {2003}, ISSN = {0556-2821}, url = {http://arxiv.org/abs/hep-ph/0306139}, Abstract = {Recent observations of the spectrum of J/ψ produced in e+e- collisions at the Υ(4S) resonance are in conflict with fixed-order calculations using the nonrelativistic QCD effective field theory. One problem is that leading order color-octet mechanisms predict an enhancement of the cross section for J/ψ with a 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/ψ 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. © The American Physical Society.}, Doi = {10.1103/PhysRevD.68.094011}, Key = {fds287671} } @article{fds287672, Author = {Mehen, T and Wecht, B}, Title = {Gauge Fields and Scalars in Rolling Tachyon Backgrounds}, Journal = {JHEP 0302}, Volume = {7}, Number = {2}, 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 = {fds287672} } @article{fds305718, Author = {Mehen, T and Wecht, B}, Title = {Gauge fields and scalars in rolling tachyon backgrounds}, Journal = {Journal of High Energy Physics}, Volume = {7}, Number = {2}, Pages = {1313-1326}, Year = {2003}, 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 those of massless particles. © SISSA/ISAS 2003.}, Key = {fds305718} } @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{fds287631, Author = {Braaten, E and Hammer, H-W and Mehen, T}, Title = {Dilute Bose-Einstein condensate with large scattering length}, Journal = {Physical Review Letters}, Volume = {88}, Number = {4}, Pages = {404011-404014}, Year = {2002}, url = {http://arxiv.org/abs/cond-mat/0108380}, Abstract = {A dilute Bose gas of atoms with large scattering length as compared to their range of interaction was studied. The energy density of a homogenous Bose-Einstein condensate (BEC) was calculated up to the second order in the low-density expansion. The instability due to three-body recombination was reflected by the imaginary part of a second order correction to energy density. The coefficient of the three body mean-field term in energy density was calculated which was found to be very large for Efimov state near threshold.}, Key = {fds287631} } @article{fds287632, Author = {Braaten, E and Jia, Y and Mehen, T}, Title = {Leading-particle effect from heavy-quark recombination}, Journal = {Physical Review Letters}, Volume = {89}, Number = {12}, Pages = {1220021-1220024}, Year = {2002}, ISSN = {0031-9007}, Abstract = {The leading particle effect was presented quantitatively and economically by the heavy-quark recombination mechanism. It was found that the leading particle effect in charm hadroproduction is an enhancement of the cross section for a charmed hadron in the forward direction of the beam. The D+/D- asymmetry was also found to fit using a single parameter whose value was consistent with a determination from charm photoproduction.}, Key = {fds287632} } @article{fds287659, Author = {Braaten, E and Yu, J and Mehen, T}, Title = {B production asymmetries in perturbative QCD}, Journal = {Physical Review D: Particles, Fields, Gravitation and Cosmology}, Volume = {66}, Number = {3}, Year = {2002}, ISSN = {0556-2821}, url = {http://arxiv.org/abs/hep-ph/0108201}, Abstract = {This paper explores a new mechanism for B production in which a b̄ quark combines with a light parton from the hard-scattering process before hadronizing into the 5 hadron. This heavy-quark recombination mechanism can be calculated within perturbative QCD up to a few nonperturbative constants. Though suppressed at large transverse momentum by a factor ∧ QCDm b/p ⊥2 relative to b̄ fragmentation production, it can be important at large rapidities. A signature for this heavy-quark recombination mechanism in pp̄ 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. © 2002 The American Physical Society.}, Doi = {10.1103/PhysRevD.66.034003}, Key = {fds287659} } @article{fds287660, Author = {Manohar, AV and Mehen, T and Pirjol, D and Stewart, IW}, Title = {Reparameterization invariance for collinear operators}, Journal = {Physics Letters B}, Volume = {539}, Number = {1-2}, Pages = {59-66}, Year = {2002}, ISSN = {0370-2693}, 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 n̄. Invariance of SCET under small changes in n and/or n̄ 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. ©2002 Elsevier Science B.V. All rights reserved.}, Doi = {10.1016/S0370-2693(02)02029-4}, Key = {fds287660} } @article{fds287673, Author = {Braaten, E and Jia, Y and Mehen, T}, Title = {Charm-anticharm asymmetries in photoproduction from heavy-quark recombination}, Journal = {Physical Review D: Particles, Fields, Gravitation and Cosmology}, Volume = {66}, Number = {1 II}, Pages = {140031-1400310}, Year = {2002}, ISSN = {0556-2821}, 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 hardscattering 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 = {fds287673} } @article{fds287692, Author = {Hammer, H-W and Mehen, T}, Title = {Range corrections to doublet S-wave neutron-deuteron scattering}, Journal = {Physics Letters B}, Volume = {516}, Number = {3-4}, Pages = {353-361}, Year = {2001}, ISSN = {0370-2693}, url = {http://dx.doi.org/10.1016/S0370-2693(01)00918-2}, 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. © 2001 Elsevier Science B.V. All rights reserved.}, Doi = {10.1016/S0370-2693(01)00918-2}, Key = {fds287692} } @article{fds287693, Author = {Hammer, H-W and Mehen, T}, Title = {A renormalized equation for the three-body system with short-range interactions}, Journal = {Nuclear Physics A}, Volume = {690}, Number = {4}, Pages = {535-546}, Year = {2001}, url = {http://dx.doi.org/10.1016/S0375-9474(00)00710-7}, 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. © 2001 Elsevier Science B.V.}, Doi = {10.1016/S0375-9474(00)00710-7}, Key = {fds287693} } @article{fds322013, Author = {Fleming, S and Mehen, T and Stewart, IW}, Title = {NN scattering^{3}S1 -^{3}D1 mixing angle at next-to-next-to-leading order}, Journal = {Physical Review C - Nuclear Physics}, Volume = {61}, Number = {4}, Pages = {440051-440059}, Year = {2000}, Month = {January}, Abstract = {The 3 S 1 - 3 D 1 mixing angle for nucleon-nucleon scattering ∈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 ∈1 well for momenta less than∼50 MeV. Including pions perturbatively significantly improves the agreement with data for momenta up to ∼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 nonperturbatively. 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 = {fds322013} } @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{fds287630, Author = {Mehen, T and Stewart, IW and Wise, MB}, Title = {The physics of the centrality dependence of elliptic flow}, Journal = {Physics Letters B}, Volume = {474}, Number = {1-2}, Pages = {27-32}, Year = {2000}, ISSN = {0370-2693}, url = {http://dx.doi.org/10.1016/S0370-2693(00)00017-4}, Abstract = {The centrality dependence of elliptic flow and how it is related to the physics of expansion of the system created in high energy nuclear collisions is discussed. Since in the hydro limit the centrality dependence of elliptic flow is mostly defined by the elliptic anisotropy of the overlapping region of the colliding nuclei, and in the low density limit by the product of the elliptic anisotropy and the multiplicity, we argue that the centrality dependence of elliptic flow should be a good indicator of the degree of equilibration reached in the reaction. Then we analyze experimental data obtained at AGS and SPS energies. The observed difference in the centrality dependence of elliptic flow could imply a transition from a hadronic to a partonic nature of the system evolution. Finally we exploit the multiplicity dependence of elliptic flow to make qualitative predictions for RHIC and LHC. (C) 2000 Published by Elsevier Science B.V.}, Doi = {10.1016/S0370-2693(00)00017-4}, Key = {fds287630} } @article{fds287682, Author = {Mehen, T and Stewart, IW}, Title = {Radiation pions in two-nucleon effective field theory}, Journal = {Nuclear Physics A}, Volume = {665}, Number = {1-2}, 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 Qr = √ MNmπ. We show that radiation pions can be included systematically with a power counting in Qr. 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. © 2000 Elsevier Science B.V. All rights reserved.}, Key = {fds287682} } @article{fds287684, Author = {Fleming, S and Mehen, T and Stewart, IW}, Title = {The NN Scattering $^3S_1-{}^3D_1$ Mixing Angle at NNLO}, Journal = {Phys. Rev. C}, Volume = {61}, Number = {4}, 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 = {fds287684} } @article{fds287685, Author = {Mehen, T and Stewart, IW and Wise, MB}, 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 = {fds287685} } @article{fds287686, Author = {Fleming, S and Mehen, T and Stewart, IW}, Title = {NNLO corrections to nucleon-nucleon scattering and perturbative pions}, Journal = {Nuclear Physics A}, Volume = {677}, Number = {1-4}, 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, 3P0,1,2, 1D2, and 3D2,3 phase shifts at this order are also compared with data. The calculations treat pions perturbatively and include the NNLO contributions from order Qr3 and Qr4 radiation pion graphs. In the 3S1, 3D1 and 3P0,2 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. © 2000 Elsevier Science B.V.}, Key = {fds287686} } @article{fds287687, Author = {Gomis, J and Kleban, M and Mehen, T and Rangamani, M and Shenker, S}, Title = {Noncommutative Gauge Dynamics from the String World Sheet}, Journal = {JHEP}, Volume = {8}, Number = {8 PART A}, 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 = {fds287687} } @article{fds287688, Author = {Gomis, J and Mehen, T}, Title = {Space-time noncommutative field theories and unitarity}, Journal = {Nuclear Physics B}, Volume = {591}, Number = {1-2}, 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. © 2000 Elsevier Science B.V.}, Key = {fds287688} } @article{fds287689, Author = {Gomis, J and Mehen, T and Wise, MB}, Title = {Quantum Field Theories with Compact Noncommutative Extra Dimensions}, Journal = {JHEP}, Volume = {8}, Number = {8 PART B}, 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 = {fds287689} } @article{fds287690, Author = {Aharony, O and Gomis, J and Mehen, T}, Title = {On Theories with Lightlike Noncommutativity}, Journal = {JHEP}, Volume = {9}, Number = {9 PART A}, 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 = {fds287690} } @article{fds287691, Author = {Mehen, T and Wise, MB}, Title = {Generalized *-Products, Wilson Lines and the Solution of the Seiberg-Witten Equations}, Journal = {JHEP}, Volume = {12}, Number = {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 = {fds287691} } @article{fds305713, Author = {Gomis, J and Mehen, T and Wise, MB}, Title = {Quantum field theories with compact non-commutative extra dimensions}, Journal = {Journal of High Energy Physics}, Volume = {4}, Number = {8 PART B}, Pages = {1-15}, Year = {2000}, Abstract = {We study field theories on spaces with additional compact noncommutative dimensions. As an example, we study φ3 on ℝ1,3xdouble-struck T signθ2 using perturbation theory. The infrared divergences in the non-compact theory give rise to unusual dynamics for the mode of φ 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 = {fds305713} } @article{fds305714, Author = {Gomis, J and Mehen, T and Rangamani, M and Kleban, M and Shenker, S}, Title = {Non-commutative gauge dynamics from the string worldsheet}, Journal = {Journal of High Energy Physics}, Volume = {4}, Number = {8 PART A}, Pages = {1-18}, Year = {2000}, Abstract = {We show how string theory can be used to reproduce the one-loop two-point photon amplitude in non-commutative 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 non-commutative field theory do not come from closed string modes in any simple way.}, Key = {fds305714} } @article{fds305715, Author = {Mehen, T and Wise, MB}, Title = {Generalized *-products, Wilson lines and the solution of the Seiberg-Witten equations}, Journal = {Journal of High Energy Physics}, Volume = {4}, Number = {12}, Pages = {XVII-9}, Year = {2000}, Abstract = {Higher order terms in the effective action of non-commutative gauge theories exhibit generalizations of the *-product (e.g. *′ and *3). These terms do not manifestly respect the non-commutative 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 non-commutative gauge transformations, but contain an infinite number of powers of the non-commutative gauge field. One example is an open Wilson line. Another is the expression for a commutative field strength tensor Fab in terms of the non-commutative gauge field Âa. Seiberg and Witten derived differential equations that relate commutative and non-commutative gauge transformations, gauge fields and field strengths. In the U(1) case we solve these equations neglecting terms of fourth order in Â but keeping all orders in the non-commutative parameter θkl.}, Key = {fds305715} } @article{fds305716, Author = {Aharony, O and Gomis, J and Mehen, T}, Title = {On theories with light-like noncommutativity}, Journal = {Journal of High Energy Physics}, Volume = {4}, Number = {9 PART A}, Pages = {XXXII-14}, Year = {2000}, Abstract = {We show that field theories with light-like noncommutativity, that is with θ0i = θ1i, 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 non-commutative 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 non-commutative field theory deformation of the (2,0) SCFT of M5-branes, while the D5-brane case leads to a non-commutative variation of "little string theories". We discuss the DLCQ description of these theories.}, Key = {fds305716} } @article{fds305717, Author = {Fleming, S and Mehen, T and Stewart, IW}, Title = {NN scattering^{3}S_{1}-^{3}D_{1}mixing angle at next-to-next-to-leading order}, Journal = {Physical Review C - Nuclear Physics}, Volume = {61}, Number = {4}, Pages = {440051-440059}, Year = {2000}, Abstract = {The 3S1-3D1 mixing angle for nucleon-nucleon scattering ∈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 ∈1 well for momenta less than∼50 MeV. Including pions perturbatively significantly improves the agreement with data for momenta up to ∼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 nonperturbatively. 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 = {fds305717} } @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{fds287680, Author = {Mehen, T and Stewart, IW}, Title = {A momentum subtraction scheme for two-nucleon effective field theory}, Journal = {Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics}, Volume = {445}, Number = {3-4}, Pages = {378-386}, Year = {1999}, Abstract = {We introduce a momentum subtraction scheme which obeys the power counting of Kaplan, Savage, and Wise (KSW), developed for systems with large scattering lengths, a. Unlike the power divergence subtraction scheme, coupling constants in this scheme obey the KSW scaling for μR > 1/a. We comment on the low-energy theorems derived by Cohen and Hansen. We conclude that there is no obstruction to using perturbative pions for momenta p > mπ. © 1999 Elsevier Science B.V. All rights reserved.}, Key = {fds287680} } @article{fds287681, Author = {Mehen, T and Stewart, IW}, Title = {Renormalization schemes and the range of two-nucleon effective field theory}, Journal = {Physical Review C - Nuclear Physics}, Volume = {59}, Number = {5}, Pages = {2365-2383}, Year = {1999}, Abstract = {The off-shell momentum subtraction (OS) and power divergence subtraction (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 μR. An error analysis indicates that the range of the theory with perturbative pions is consistent with 500 MeV.}, Key = {fds287681} } @article{fds287683, Author = {Mehen, T and Stewart, IW and Wise, MB}, Title = {Wigner symmetry in the limit of large scattering lengths}, Journal = {Physical Review Letters}, Volume = {83}, Number = {5}, 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 → NN axion and γd → np are also considered. © 1999 The American Physical Society.}, Key = {fds287683} } @booklet{Fleming98, Author = {Fleming, S and Mehen, T}, Title = {Photoproduction of h(c)}, Journal = {Physical Review D}, Volume = {5803}, Number = {3}, Pages = {art. no.-037503}, Year = {1998}, Month = {August}, ISSN = {0556-2821}, Abstract = {Using the NRQCD factorization formalism, we calculate the total cross section for the photoproduction of h c mesons. We include color-octet and color-singlet mechanisms as well as next-to-leading order perturbative QCD corrections. The theoretical prediction depends on two nonperturbative matrix elements that are not well determined from existing data on charmonium production. For reasonable values of these matrix elements, the cross section is large enough that the h c may be observable at the E831 experiment and at the DESY HERA experiments.}, Key = {Fleming98} } @booklet{Mehen98, Author = {Mehen, T}, 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}, Abstract = {Order Î²0nÎ±sn+1 QCD corrections to top quark decays into W+ and H+ bosons are computed to all orders in perturbation theory. Predictions for the radiative corrections to the top quark width are compared with the estimates from BLM scale setting procedures. The results of the summation are shown to greatly improve understanding of higher order corrections in the limit mW, mH â†’ mt, where the BLM scale setting method is known to fail. Attempts to reduce nonperturbative error by substituting the running mass for the pole mass in the expression for the decay are shown to fail in the limit mW, mH â†’ mt because of subtleties in the treatment of phase space. Â© 1998 Published by Elsevier Science B.V.}, Key = {Mehen98} } @booklet{Fleming98a, Author = {Fleming, S and Mehen, T}, Title = {Leptoproduction of J/ψ}, Journal = {Physical Review D - Particles, Fields, Gravitation and Cosmology}, Volume = {57}, Number = {3}, Pages = {1846-1857}, Year = {1998}, Abstract = {We study leptoproduction of J/ψ at large Q2 within the nonrelativistic QCD (NRQCD) factorization formalism. The cross section is dominated by color-octet terms that are of order αs. The color-singlet term, which is of order α2s, is shown to make a small contribution to the total cross section. We also calculate the tree diagrams for color-octet production at order α2s in a region of phase space where there is no leading color-octet contribution. We find that in this regime the color-singlet contribution dominates. We argue that nonperturbative corrections arising from diffractive leptoproduction, higher twist effects, and higher order terms in the NRQCD velocity expansion should be suppressed as Q2 is increased. Therefore, the color-octet matrix elements 〈script O signψ8(1S0)〉 and 〈script O signψ8(3P0)〉 can be reliably extracted from this process. Finally, we point out that an experimental measurement of the polarization of leptoproduced J/ψ will provide an excellent test of the NRQCD factorization formalism.}, Key = {Fleming98a} } @article{fds305712, Author = {Fleming, S and Mehen, T}, Title = {Photoproduction of h_{c}}, Journal = {Physical Review D: Particles, Fields, Gravitation and Cosmology}, Volume = {58}, Number = {3}, Pages = {0375031-0375034}, Year = {1998}, ISSN = {0556-2821}, Abstract = {Using the NRQCD factorization formalism, we calculate the total cross section for the photoproduction of hc mesons. We include color-octet and color-singlet mechanisms as well as next-to-leading order perturbative QCD corrections. The theoretical prediction depends on two nonperturbative matrix elements that are not well determined from existing data on charmonium production. For reasonable values of these matrix elements, the cross section is large enough that the hc may be observable at the E831 experiment and at the DESY HERA experiments.}, Key = {fds305712} } @article{fds305711, Author = {Mehen, T}, Title = {Summing O( β_{0}^{n}α_{s}^{n+1}) corrections to top quark decays}, Journal = {Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics}, Volume = {417}, Number = {3-4}, Pages = {353-360}, Year = {1998}, url = {http://dx.doi.org/10.1016/S0370-2693(97)01348-8}, Abstract = {Order β0nαsn+1 QCD corrections to top quark decays into W+ and H+ bosons are computed to all orders in perturbation theory. Predictions for the radiative corrections to the top quark width are compared with the estimates from BLM scale setting procedures. The results of the summation are shown to greatly improve understanding of higher order corrections in the limit mW, mH → mt, where the BLM scale setting method is known to fail. Attempts to reduce nonperturbative error by substituting the running mass for the pole mass in the expression for the decay are shown to fail in the limit mW, mH → mt because of subtleties in the treatment of phase space. © 1998 Published by Elsevier Science B.V.}, Doi = {10.1016/S0370-2693(97)01348-8}, Key = {fds305711} } @booklet{Mehen97, Author = {Mehen, T}, Title = {Testing quarkonium production with photoproduced JlΨ+ γ}, Journal = {Physical Review D - Particles, Fields, Gravitation and Cosmology}, Volume = {55}, Number = {7}, Pages = {4338-4343}, Year = {1997}, Abstract = {I compute the leading color-octet contributions to the process γ+p→JlΨ+ γ(+Χ) within the nonrelativistic QCD (NRQCD) factorization formalism. In the color-singlet model, JlΨ+ γ can only be produced when the photon interacts through its structure function, while the color-octet mechanism allows for production of Jl Ψ+ γ via direct photon-gluon fusion. Resolved photon processes can be distinguished easily from direct photon processes by examining the fraction of the incident photon energy carried away by the Jl Ψ in the event. Therefore, this process provides a conclusive test of the color-octet mechanism. Jl Ψ+ γ production is particularly sensitive to the NRQCD matrix element which figures prominently in the fragmentation production of Jl Ψ at large p⊥ in hadron colliders. I also examine the predictions of the color evaporation model (CEM) of quarkonium production and find that this process can easily discriminate between the NRQCD factorization formalism and the CEM.}, Key = {Mehen97} } @booklet{Falk96, Author = {Falk, AF and Mehen, T}, Title = {Excited heavy mesons beyond leading order in the heavy quark expansion}, Journal = {Physical Review D - Particles, Fields, Gravitation and Cosmology}, Volume = {53}, Number = {1}, Pages = {231-240}, Year = {1996}, Abstract = {We examine the decays of excited heavy mesons, including the leading power corrections to the heavy quark limit. We find a new and natural explanation for the large deviation of the width of the D1 (2420) from the heavy quark symmetry prediction. Our formalism leads to detailed predictions for the properties of the excited bottom mesons, some of which recently have been observed. Finally, we present a detailed analysis of the effect of power corrections and finite meson widths on the angular distributions which may be measured in heavy meson decays.}, Key = {Falk96} } @booklet{Mehen96, Author = {Mehen, T}, Title = {Scale setting in top quark decays}, Journal = {Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics}, Volume = {382}, Number = {3}, Pages = {267-272}, Year = {1996}, url = {http://dx.doi.org/10.1016/0370-2693(96)00681-8}, Abstract = {We compute the O(β0α2s) QCD corrections to the Standard Model decay t → W+ b as well as the non standard decay t → H+ b. We then use our results to compute the BLM scale for these decays, and study the dependence of the BLM scale on the mass of the boson in the decay. We find that the BLM procedure gives extremely small scales when top decays into heavy bosons. When we try to improve the BLM scale by reexpressing rates as a functions of the top quark running mass, we find the BLM scale exhibits unnatural dependence on the boson mass, casting doubts on the applicability of the BLM procedure to these processes.}, Doi = {10.1016/0370-2693(96)00681-8}, Key = {Mehen96} } %% Papers Accepted @article{fds225631, Author = {Thomas Mehen}, Title = {Exotic Quarkonium Spectroscopy: X(3872) Z(10610) Z(10650) in Non-Relativistic Effective Theory}, Journal = {Conference Proeceedings for PhiPsi 2013, Rome, Italy, September 11, 2013}, Year = {2013}, Key = {fds225631} } %% Preprints @article{fds287641, Author = {Kim, C and Mehen, T}, Title = {Octetonium at the LHC}, Journal = {Nuclear Physics, Section B: Proceedings Supplements}, Volume = {200-202}, Number = {1 C}, Pages = {179-182}, Year = {2010}, ISSN = {0920-5632}, url = {http://arXiv.org/abs/0909.5695}, Abstract = {Several models of new physics, such as grand unified theories, Pati-Salam models, chiral color models, etc., predict the existence of an SU(2)L doublet of color-octet scalars (COS). In the Manohar-Wise model, the Yukawa couplings of the COS are assumed to be consistent with Minimal Flavor Violation ensuring constraints from flavor physics are satisfied even for relatively light scalars. In this simple model we consider the production of color singlet bound states of COS that we call octetonium. Octetonium are mainly produced via gluon-gluon fusion and have significant production cross sections at the LHC. They can decay to pairs of gluons or electroweak gauge bosons. If the masses of the octetonia are 1 TeV or less, these states will be visible as resonances in γγ, W+W-, ZZ, and γZ. © 2010 Elsevier B.V.}, Doi = {10.1016/j.nuclphysbps.2010.02.081}, Key = {fds287641} } @article{fds287640, Author = {Fleming, S and Mehen, T}, Title = {X(3872) in effective field theory}, Journal = {AIP Conference Proceedings}, Volume = {1182}, Pages = {491-494}, Year = {2009}, ISSN = {0094-243X}, url = {http://arXiv.org/abs/0907.4142}, Abstract = {If the X(3872) resonance is a shallow boundstate of a the charm mesons D0D̄*0 and D*0D̄0 it can be described by an effective theory of nonrelativistic D mesons coupled to nonrelativistic pions (X-EFT). In this talk, I give a brief overview of the X(3872), followed by a short review of X-EFT. I end my talk with results from calculations of the the next-to-leading-order correction to the partial decay width Γ[X→ D0D̄0π0], and the decay of X(3872) to P-wave quarkonia. © 2009 American Institute of Physics.}, Doi = {10.1063/1.3293853}, Key = {fds287640} }