Mon·Sep 24, 2007Monday·September 24, 2007

1. 01*

   Nucleon form factors on the lattice with light dynamical fermions

   UKQCDSF Collaboration: Meinulf Gockeler🇩🇪 · Philipp Hagler🇩🇪 · Roger Horsley🇬🇧 · Yoshifumi Nakamura🇩🇪 · Munehisa Ohtani🇩🇪 · Dirk Pleiter🇩🇪 · Paul E. L. Rakow🇬🇧 · Andreas Schafer🇩🇪 · Gerrit Schierholz · Wolfram Schroers🇩🇪 · Hinnerk Stuben🇩🇪 · James M. Zanotti🇬🇧

   The electromagnetic form factors provide important insight into the internal structure of the nucleon and continue to be of major interest for experiment and phenomenology. For an intermediate range of momenta the form factors can be calculated on the lattice. However, the reliability of the results is limited by systematic errors mostly due to the required extrapolation to physical quark masses. Chiral effective field theories predict a rather strong quark mass dependence in a range which was yet inaccessible for lattice simulations. We give an update on recent results from the QCDSF collaboration using gauge configurations with dynamical Nf=2, non-perturbatively O(a)-improved Wilson fermions at pion masses as low as 350 MeV.

   hep-lat14 citations
2. 02*

   Luescher-Weisz algorithm for excited states of the QCD flux-tube

   Bastian B. Brandt🇩🇪 · Pushan Majumdar🇩🇪

   We present a version of the Luescher-Weisz multilevel algorithm ideally suited for studying excited states of the QCD flux tube. While the original version achieved error reduction only in the temporal direction, the new algorithm reduces fluctuations in the sources as well. We report on the implementation of this algorithm as well as improvement over the older method. We also present first results, where we see a good agreement with theoretical predictions from bosonic string models.

   hep-latPoS(2007)·6 citations
3. 03*

   Exploring the transition into the Chiral Regime of QCD using the Interacting Instanton Liquid Model

   M. Cristoforetti🇮🇹 · P. Faccioli🇮🇹 · M. Traini🇮🇹 · J. W. Negele🇺🇸

   The non-perturbative quark-gluon interaction depends significantly on the value of the quark mass. In particular, in the light quark mass regime, correlations are strongly influenced by dynamics associated to chiral symmetry breaking. We use the Interacting Instanton Liquid Model (IILM) as a tool to investigate the microscopic dynamical mechanisms which underly the dependence on the quark mass and drive the transition into the chiral regime of QCD. To ensure the validity of the model, we first verify that the dependence on the quark mass for several observables calculated in the IILM agrees well with the predictions of chiral perturbation theory and with lattice simulations. We then show that a quark mass m*~80 MeV emerging naturally from the model specifies the mass scale above which the dynamics associated with low-lying eigenmodes of the Direac operator becomes sub-leading and the contribution of the fermion determinant is suppressed.

   hep-lathep-phPoS(2007)·1 citation
4. 04*

   Probing the ground state in gauge theories

   T. Heinzl🇬🇧 · A. Ilderton🇬🇧 · K. Langfeld🇬🇧 · M. Lavelle🇬🇧 · W. Lutz🇬🇧 · D. McMullan🇬🇧

   We consider two very different models of the flux tube linking two heavy quarks: a string linking the matter fields and a Coulombic description of two separately gauge invariant charges. We compare how close they are to the unknown true ground state in compact U(1) and the SU(2) Higgs model. Simulations in compact U(1) show that the string description is better in the confined phase but the Coulombic description is best in the deconfined phase; the last result is shown to agree with analytical calculations. Surprisingly in the non-abelian theory the Coulombic description is better in both the Higgs and confined phases. This indicates a significant difference in the width of the flux tubes in the two theories.

   hep-lathep-phhep-thPRD(2008)·15 citations
5. 05*

   Phase Transitions and the Perfectness of Fluids

   Jiunn-Wei Chen🇹🇼 · Mei Huang🇨🇳 · Yen-Han Li🇹🇼 · Eiji Nakano🇹🇼 · Di-Lun Yang🇹🇼

   We calculate the ratio eta/s, the shear viscosity (eta) to entropy density (s), which characterizes how perfect a fluid is, in weakly coupled real scalar field theories with different types of phase transitions. The mean-field results of the eta/s behaviors agree with the empirical observations in atomic and molecular systems such as water, He, N, and all the matters with data available in the NIST database. These behaviors are expected to be the same in N component scalar theories with an O(N) symmetry. We speculate these eta/s behaviors are general properties of fluid shared by QCD and cold atoms. Finally, we clarify some issues regarding counterexamples of the conjectured universal eta/s bound found in Refs.[16,17].

   ↳ hep-phcond-mat.othercond-mat.softhep-lat+2PLB(2008)·50 citations

* 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.