Fri·Sep 3, 2004Friday·September 3, 2004

1. 01*

   QCD Thermodynamics: Lattice Results confront Models

   M. D'Elia🇮🇹 · M.P. Lombardo🇮🇹

   We show that lattice results on four flavor QCD at nonzero temperature and baryon density compare well with the hadron resonance gas model up to T approx. 0.95 Tc, and approach a free field behaviour with a reduced effective number of flavor for T \ge 1.5 Tc. Chiral symmetry and confinement are interrelated, and we note analogies between the critical line of QCD and that of simple models with the same global symmetries.

   hep-lat4 citations
2. 02*

   Extracting excited states from lattice QCD: the Roper resonance

   D. Guadagnoli🇮🇹 · M. Papinutto🇩🇪 · S. Simula🇮🇹

   We present a new method for extracting excited states from a single two-point correlation function calculated on the lattice. Our method simply combines the correlation function evaluated at different time slices so as to ``subtract'' the leading exponential decay (ground state) and to give access to the first excited state. The method is applied to a quenched lattice study (volume = 24^3 x 64, beta = 6.2, 1/a = 2.55 GeV) of the first excited state of the nucleon using the local interpolating operator O = [uT C gamma5 d] u. The results are consistent with the identification of our extracted excited state with the Roper resonance N'(1440). The switching of the level ordering with respect to the negative-parity partner of the nucleon, N*(1535), is not seen at the simulated quark masses and, basing on crude extrapolations, is tentatively expected to occur close to the physical point.

   hep-lathep-phnucl-thPLB(2004)·44 citations
3. 03*

   Wilson-like fermions and the static B_B parameter with no chirality breaking mixings

   Michele Della Morte🇩🇪

   I consider the recent proposal by R. Frezzotti and G. Rossi to chirally improve Wilson fermions in such a way that mixings among operators of different chirality can be excluded. The method, which is based on the use of twisted mass QCD with several replica of valence quarks, is extended here to static-light systems. The operators relevant for the computation of the B_B parameter (in the static approximation) are discussed. In this case the same renormalization pattern as for Ginsparg-Wilson fermions is obtained by a simple modification of the discretization of the action for valence quarks.

   hep-latNucl.Phys.B Proc.Suppl.(2005)·9 citations
4. 04*

   Testing universality and the fractional power prescription for the staggered fermion determinant

   David H. Adams🇳🇱

   In [Phys.Rev.Lett.92:162002 (2004), hep-lat/0312025] expressions for the continuous Euclidean time limits of various lattice fermion determinants were derived and compared in order to test universality expectations in Lattice QCD. Here we review that work with emphasis on its relevance for assessing the fractional power prescription for the determinant in dynamical staggered fermion simulations. Some new supplementary material is presented; in particular the status of the "universality anomaly" is clarified: it is shown to be gauge field-independent and therefore physically inconsequential.

   hep-lathep-thmath-phmath.MPNucl.Phys.B Proc.Suppl.(2005)·18 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.