Mon·Oct 1, 2007Monday·October 1, 2007

1. 01*

   Universal properties of large N phase transitions in Wilson loops

   R. Narayanan (FIU)🇺🇸 · H. Neuberger (Rutgers)🇺🇸

   Numerical studies support the conjecture that in continuum planar QCD the eigenvalue density of a Wilson loop operator undergoes a transition as the loop is dilated while keeping the loop shape fixed. A second part of the conjecture is that the transition obeys large N universality and that this universality class is the same in 2, 3 and 4 Euclidean space-time dimensions. The focus of the talk will be on clarifying precisely what the conjecture is claiming.

   hep-latPoS(2007)·4 citations
2. 02*

   Higgs mechanism in five-dimensional gauge theories

   Magdalena Luz🇩🇪 · Nikos Irges🇬🇷 · Francesco Knechtli🇩🇪

   Lattice simulations of five-dimensional gauge theories on an orbifold revealed that there is spontaneous symmetry breaking. Some of the extra-dimensional components of the gauge field play the role of a Higgs field and some of the four-dimensional components become massive gauge bosons. The effect is confirmed by computing the Coleman-Weinberg potential with a cutoff. We compare the results of this computation with the lattice data.

   hep-lathep-phPoS(2007)·3 citations
3. 03*

   Neutral mesons and disconnected diagrams in Twisted Mass QCD

   ETM Collaboration: Chris Michael🇬🇧 · Carsten Urbach🇬🇧

   We evaluate properties of neutral mesons in Nf=2 dynamical simulations of TMQCD at maximal twist. The pion is explored - establishing the size of the isospin splitting (an order a^2 effect). We investigate the eta' (the Nf=2 flavour singlet pseudoscalar meson) and neutral rho and scalar mesons. We show that disconnected diagrams can be evaluated very efficiently in TMQCD using variance reduction methods.

   hep-latPoS(2007)·55 citations
4. 04*

   Light quark masses and pseudoscalar decay constants from Nf=2 Lattice QCD with twisted mass fermions

   B. Blossier · Ph. Boucaud · P. Dimopoulos · F. Farchioni · R. Frezzotti · V. Gimenez · G. Herdoiza · K. Jansen · V. Lubicz · C. Michael · D. Palao · M. Papinutto and 6 other authors

   We present the results of a lattice QCD calculation of the average up-down and strange quark masses and of the light meson pseudoscalar decay constants with Nf=2 dynamical fermions. The simulation is carried out at a single value of the lattice spacing with the twisted mass fermionic action at maximal twist, which guarantees automatic O(a)-improvement of the physical quantities. Quark masses are renormalized by implementing the non-perturbative RI-MOM renormalization procedure. Our results for the light quark masses are m_ud^{msbar}(2 GeV)= 3.85 +- 0.12 +- 0.40 MeV, m_s^{msbar}(2 GeV) = 105 +- 3 +- 9 MeV and m_s/m_ud = 27.3 +- 0.3 +- 1.2. We also obtain fK = 161.7 +- 1.2 +- 3.1 MeV and the ratio fK/fpi=1.227 +- 0.009 +- 0.024. From this ratio, by using the experimental determination of Gamma(K-> mu nu (gamma))/Gamma(pi -> mu nu (gamma)) and the average value of |Vud| from nuclear beta decays, we obtain |Vus|=0.2192(5)(45), in agreement with the determination from Kl3 decays and the unitarity constraint.

   hep-lathep-phJHEP(2008)·114 citations
5. 05*

   Dynamical Chirally Improved Quarks: First Results for Hadron Masses

   R. Frigori🇦🇹 · Ch. Gattringer🇦🇹 · C. B. Lang🇦🇹 · M. Limmer🇦🇹 · T. Maurer🇩🇪 · D. Mohler🇦🇹 · A. Schäfer🇩🇪

   We present first results for a study with two mass-degenerate dynamical Chirally Improved (CI) fermions on lattices of spatial extent 2.4 fm. The CI Dirac operator obeys the Ginsparg-Wilson condition in good approximation. The pion mass we use is still large O(470 MeV) for the 16**3*32 lattices with lattice spacing of 0.15 fm. The hadron masses are obtained with the variational technique and the results compared with earlier quenched calculations with similar lattice parameters. We find indications for the isovector, scalar meson a0(980) near the experimental value, in contradistinction to quenched results which always produced a mass value compatible with the first excitation a0(1450).

   hep-latPoS(2007)·30 citations
6. 06*

   Coulomb gauge studies of SU(3) Yang-Mills theory on the lattice

   Aiko Voigt🇩🇪 · Ernst-Michael Ilgenfritz🇩🇪 · Michael Mueller-Preussker🇩🇪 · Andre Sternbeck🇦🇺

   We study the infrared behaviour of lattice SU(3) Yang-Mills theory in Coulomb gauge in terms of the ghost propagator, the Coulomb potential and the transversal and the time-time component of the equal-time gluon propagator. In particular, we focus on the Gribov problem and its impact on the observables. We observe that the simulated annealing method is advantageous for fixing the Coulomb gauge in large volumes. We study finite size and discretization effects. While finite size effects can be controlled by the cone cut, and the ghost propagator and the Coulomb potential become scaling functions with the cylinder cut, the equal-time gluon propagator does not show scaling in the considered range of the inverse coupling constant. The ghost propagator is infrared enhanced. The Coulomb potential is now extended to considerably lower momenta and shows a more complicated infrared regime. The Coulomb string tension satisfies Zwanziger's inequality, but its estimate can be considered only preliminary because of the systematic Gribov effect that is particularly strong for the Coulomb potential.

   hep-latPoS(2007)·22 citations
7. 07*

   Worldline Approach to Chiral Fermions

   Kurt Langfeld🇬🇧 · Gerald Dunne🇺🇸 · Holger Gies🇩🇪 · Klaus Klingmuller🇩🇪

   We propose to apply ``worldline numerics'' to a numerical calculation of quark determinants. The Gross-Neveu model with a U(1) chiral symmetry is considered as a first test. The worldline approach allows for an analytic renormalisation, and only finite parts of the determinant require a numerical calculation. It is shown that the discretisation of the worldlines, which is central to the numerical treatment, preserves chiral symmetry exactly. Numerical results for a kink configuration as a scalar background field are shown and compared with analytical results. The case of finite fermion chemical potential is also briefly discussed.

   hep-lathep-phhep-thPoS(2007)·5 citations
8. 08*

   Precision Lattice Calculation of D and Ds decay constants

   Eduardo Follana🇬🇧

   We present a determination of the decay constants of the $D$ and $D_s$ mesons from lattice QCD, each with a total error of about 2%, approximately a factor of three better than previous calculations. We have been able to achieve this through the use of a highly improved discretization of QCD for charm quarks, coupled to gauge configurations generated by the MILC collaboration that include the full effect of sea u, d, and s quarks. We have results for a range of u/d masses down to m_s/5 and three values of the lattice spacing, which allow us to perform accurate continuum and chiral extrapolations. We fix the charm quark mass to give the experimental value of the \eta_c mass, and then a stringent test of our approach is the fact that we obtain correct (and accurate) values for the mass of the D and D_s mesons. We compare f_D and f_{D_s} with f_K and f_\pi, and using experiment determine corresponding CKM elements with good precision.

   hep-lateConf(2007)·4 citations
9. 09*

   Domain-wall and overlap fermions at nonzero quark chemical potential

   Jacques Bloch🇩🇪 · Tilo Wettig🇩🇪

   We have recently given a construction of the overlap Dirac operator at nonzero quark chemical potential. Here, we introduce a quark chemical potential in the domain-wall fermion formalism and show that our earlier result is reproduced if the extent of the fifth dimension is taken to infinity and its lattice spacing is taken to zero. We also extend this result to include a bare quark mass, consider its continuum limit, and prove a number of properties of the overlap operator at nonzero quark chemical potential. In particular, we show that the relation between the anomaly and the index of the overlap operator remains valid.

   hep-latPRD(2007)·35 citations
10. 10*

    Spectral properties of the non-hermitian Wilson-Dirac operator in the Schroedinger functional

    Oliver Witzel🇩🇪 · Shinji Takeda🇩🇪 · Ulli Wolff🇩🇪

    We report on some preparatory investigations for the simulation of the QCD Schroedinger functional with a non-hermitian polynomial hybrid Monte Carlo algorithm. The complex spectrum of the non-hermitean free operator with SF boundary condititons is computed semianalytically. Then it is shown how one can obtain relevant information on the boundary of the spectral domain also in the presence of nontrivial gaugefields by monitoring the behavior of polynomials in the Wilson operator applied on random vectors.

    hep-latPoS(2007)·1 citation

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.