Showing papers by "Thomas Manke published in 2000"

Phase structure and critical temperature of two-flavor QCD with a renormalization group improved gauge action and clover improved Wilson quark action

Abstract: We study the finite-temperature phase structure and the transition temperature of QCD with two flavors of dynamical quarks on a lattice with the temporal size ${N}_{t}=4,$ using a renormalization group improved gauge action and the Wilson quark action improved by the clover term. The region of a parity-broken phase is identified, and the finite-temperature transition line is located on a two-dimensional parameter space of the coupling $(\ensuremath{\beta}{=6/g}^{2})$ and hopping parameter K. Near the chiral transition point, defined as the crossing point of the critical line of the vanishing pion mass and the line of finite-temperature transition, the system exhibits behavior well described by the scaling exponents of the three-dimensional $O(4)$ spin model. This indicates a second-order chiral transition in the continuum limit. The transition temperature in the chiral limit is estimated to be ${T}_{c}=171(4)$ MeV.

Dynamical quark effects on light quark masses.

Abstract: Light quark masses are calculated in lattice QCD with two degenerate flavors of dynamical quarks. The calculations are made with improved actions with lattice spacing $a\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.22$--0.11 fm. In the continuum limit we find ${m}_{\mathrm{ud}}^{\overline{\mathrm{MS}}}(2\mathrm{GeV}){\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3.44}_{\ensuremath{-}0.22}^{+0.14}\mathrm{MeV}$ using the $\ensuremath{\pi}$ and $\ensuremath{\rho}$ meson masses as physical input, and ${m}_{s}^{\overline{\mathrm{MS}}}(2\mathrm{GeV}){\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}88}_{\ensuremath{-}6}^{+4}\mathrm{MeV}$ or ${90}_{\ensuremath{-}11}^{+5}\mathrm{MeV}$ with the $K$ or $\ensuremath{\varphi}$ meson mass as additional input. The quoted errors represent statistical and systematic combined, the latter including those from continuum and chiral extrapolations, and from renormalization factors. Compared to quenched results, two flavors of dynamical quarks reduce quark masses by about $25%$.

Sea quark effects on quarkonia

Abstract: We study the effects of two dynamical sea quarks on the spectrum of heavy quarkonia. Within the non-relativistic approach to Lattice QCD we found sizeable changes to the hyperfine splitting, but we could not observe any changes for the fine structure. We also investigated the scaling behaviour of our results for several different lattice spacings.

Light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks

Abstract: We present updated results of the CP-PACS calculation of the light hadron spectrum in N f = 2 full QCD. Simulations are made with an RG-improved gauge action and a tadpole-improved clover quark action for sea quark masses corresponding to m PS / m V ≈ 0.8-0.6 and the lattice spacing a = 0.22-0.09 fm. A comparison of the N f = 2 QCD spectrum with new quenched results, obtained with the same improved action, shows clearly the existence of sea quark effects in vector meson masses. Results for light quark masses are also presented.

Eta meson mass and topology in QCD with two light flavors

Abstract: We present results for the mass of the flavor singlet meson calculated on two-flavor full QCD configurations generated by the CP-PACS full QCD project. We also investigate topological charge fluctuations and their dependence on the sea quark mass.

Quenched QCD with domain-wall fermions on coarse lattices☆

Abstract: We investigate the existence of chiral zero modes at a −1 ≅ 1 GeV in quenched domain-wall QCD. Simulations are carried out for the plaquette and an RG-improved gauge actions on a 12 3 × 24 × N s lattice with N s = 10 – 50. We find that the pion mass in the chiral limit remains non-vanishing as N s → ∞ for both gauge actions. Possible origins of this non-vanishing pion mass are discussed.

Exotic quarkonia from anisotropic lattices

Abstract: We study in detail the spectrum of heavy quarkonia with different orbital angular momentum along with their radial and gluonic excitations. Using an anisotropic formulation of Lattice QCD we achieved an unprecedented control over statistical errors and were able to study systematic errors such as lattice spacing artefacts, finite volume effects and relativistic corrections. First results on the spin structure in heavy hybrids are also presented.

Heavy quarkonia from anisotropic and isotropic lattices

Abstract: We report on recent results for the spectrum of heavy quarkonia. Using coarse and anisotropic lattices we achieved an unprecedented control over statistical and systematic errors for higher excited states such as exotic hybrid states. In a parallel study on isotropic lattices we also investigate the effect of two dynamical flavours on the spin structure of charmonium and bottomonium for several symmetric lattices.

Heavy-light decay constants from clover heavy quark action in QCD with two flavors of dynamical quarks

Abstract: We present results on an analysis of the decay constants fBd and fBs with two flavours of sea quark. The calculation has been carried out on 3 different bare gauge couplings and 4 sea quark masses at each gauge coupling, with mπ/mϱ ranging from 0.8 to 0.6. We employ the Fermilab formalism to perform calculations with heavy quarks whose mass is in the range of the b-quark. A detailed comparison with a quenched calculation using the same action is made to elucidate the effects due to the sea quarks.

Heavy-light spectrum and decay constant from NRQCD with two flavors of dynamical quarks

Abstract: We report on a study of B mesons on Nf = 2 full QCD configurations using an RG-improved gauge action, NRQCD heavy quark action and tadpole-improved clover light quark action. Results on the heavy-light spectrum and the decay constants from 163 × 32 lattices at a−1 ≈ 1.5 GeV are presented, and compared with quenched results obtained with the same action combination at matching lattice spacings.

Equation of state in finite-temperature QCD with improved Wilson quarks

Abstract: We study finite-temperature phase transition and equation of state for two-flavor QCD at N t = 4 using an RG-improved gauge action and a meanfield-improved clover quark action. The pressure is computed using the integral method. The O(4) scaling of chiral order parameter is also examined.

Equation of state for SU(3) gauge theory with RG improved action

Abstract: We present results for the equation of state for pure SU(3) gauge theory obtained with a renormalization-group (RG) improved action. The energy density and pressure are calculated on a 16 3 ×4 and a 32 3 ×8 lattice employing the integral method. Extrapolating the results to the continuum limit, we find the energy density and pressure to be in good agreement with those obtained with the standard plaquette action within the error of 3–4%.