12,662 research outputs found

    Scaling of the critical temperature and quark potential with a renormalization group improved SU(3) gauge action

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    We study the scaling property of the ratio of the critical temperature TcT_c to the square root of the string tension σ\sigma in the SU(3) pure gauge theory using a renormalization group improved action. We first determine the critical coupling βc\beta_c on lattices with temporal extension Nt=4N_t=4 and 6, and then calculate the static quark potential at the critical couplings on lattices at zero temperature. The values of Tc/σT_{c}/\sqrt{\sigma} in the infinite volume limit are identical within errors, while they are slightly larger than the value extrapolated to the continuum limit with the standard action. We also note that the rotational invariance of the static quark potential is remarkably restored in the both cases, and that the potential V(R)V(R) in physical units scales in the whole region of RR investigated.Comment: 3 pages of Latex, 5 PostScript figures, Talk presented at LATTICE96(finite temperature

    Quantum chromodynamics with various number of flavors

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    The phase structure of QCD with various number of flavors is studied for Wilson quarks. For the case of NF=3N_F=3 we find that the finite temperature deconfining transition is of first order in the chiral limit on an Nt=4N_t=4 lattice. Together with our previous results that the deconfining transition in the chiral limit is continuous for NF=2N_F=2 and is first order for NF=6N_F=6, the order of the transition is found to be consistent with a prediction of universality. The case of SU(2)SU(2) QCD is also studied in the strong coupling limit and the phase structure is found to be quite similar to the case of SU(3)SU(3): There exists a critical number of flavors NFN_F^* and for NFNFN_F \geq N_F^* the confinement is broken even in the strong coupling limit for light quarks. NF=3N_F^*=3 corresponding to 7 for SU(3)SU(3).Comment: 3 pages with 5 PS figures, LaTeX (espcrc2.sty required), UTHEP-26

    Phase structure of QCD for general number of flavors

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    We investigate and elucidate the phase structure of QCD for general number of flavors NFN_F with Wilson quarks, varying NFN_F from 2 up to 300. Based on numerical results combined with the result of the perturbation theory we propose the following picture: When NF17N_F \ge 17, there is only a trivial fixed point and therefore the theory in the continuum limit is trivial. On the other hand, when 16NF716 \ge N_F \ge 7, there is a non-trivial fixed point and therefore the theory is non-trivial with anomalous dimensions, however, without quark confinement. Theories which satisfy both quark confinement and spontaneous chiral symmetry breaking in the continuum limit exist only for NF6N_F \le 6. We also discuss the structure of the deconfining phase at finite temperatures for the small number of flavors such as NF=2N_F=2 and 3, through a systematic study of it for general number of flavors.Comment: LaTeX, 7 pages, 10 PS figures, Talk presented at LATTICE96(poster) and LATTICE96(finite temperature

    High statistics calculations of quenched QCD spectrum using various quark sources

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    We present the results for the hadron spectrum calculated on 400 configurations using point source, wall source and 8-cubic sources, in quenched QCD with Wilson fermions at β=6.0\beta=6.0 and K=0.155K=0.155 on a 243×5424^3 \times 54 lattice. The results for the ground state masses obtained with three types of quark sources agree well with each other. Masses of the first excited states appear consistent with experimental values within large errors.Comment: 3 pages, 2 postscript figures, to appear in the Proceedings of LATTICE 93, Dallas, USA; preprint UTHEP-26

    Anisotropic Improved Gauge Actions; --Perturbative and Numerical Studies --

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    The Λ\Lambda parameter on the anisotropic lattice, the spatial and temperature coupling constant gσg_{\sigma}, gτg_{\tau} and their derivative with respaect to the the anisotropy parameter ξ\xi are studied perturbatively for the class of improved actions, which cover tree level Symanzik's, Iwasaki's and QCDTARO's improved actions. The η(=gτ/gσ)\eta(=g_{\tau}/g_{\sigma}) becomes less than 1 for Iwasaki's and QCDTARO's action, which is confirmed nonperturbatively by numerical simulations. Derivatives of the coupling constants with respect to the anisotropy parameter, gτ/ξ\partial g_{\tau}/\partial \xi and gσ/ξ\partial g_{\sigma}/\partial \xi, change sign for those improved actions.Comment: LATTICE98(hightemp), 3 pages in latex, 4 Postscript figures Fonts in Fig3 is replaced Aria

    Chiral Phase Transition in Lattice QCD with Wilson Quarks

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    The nature of the chiral phase transition in lattice QCD is studied for the cases of 2, 3 and 6 flavors with degenerate Wilson quarks, mainly on a lattice with the temporal direction extension Nt=4N_t=4. We find that the chiral phase transition is continuous for the case of 2 flavors, while it is of first order for 3 and 6 flavors.Comment: uuencoded compressed tar file, LaTeX, 14 pages, 7 figure

    Transport Coefficients of Quark Gluon Plasma From Lattice Gauge Theory

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    Numerical results for the transport coefficients of quark gluon plasma are obtained by lattice simulations on on 163×816^3 \times 8 lattice with the quench approximation where we apply the gauge action proposed by Iwasaki. The bulk viscosity is consistent with zero, and the shear viscosity is slightly smaller than the typical hadron masses. They are not far from the simple extrapolation on the figure of perturbative calculation in high temperature limit down to TTcT \sim T_{c}. The gluon propagator in the confined and deconfined phases are also discussed.Comment: Quark Matter 97(talk at parallel session QCD) 4 pages in latex, 4 Postscript figure

    Hadron spectroscopy and static quark potential in full QCD: A comparison of improved actions on the CP-PACS

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    We present first results from a full QCD calculation on the CP-PACS, comparing various actions at a11GeVa^{-1} \sim 1 GeV and mπ/mρ0.7m_\pi/m_\rho \approx 0.7--0.9. We use the plaquette and a renormalization group improved action for the gluons, and the Wilson and the SW-Clover action for quarks. We find that significant improvements in the hadron spectrum results from improving the quarks, while the gluon improvement is required for a rotationally invariant static potential. An ongoing effort towards exploring the chiral limit in full QCD is described.Comment: 6 pages, based on talks presented by R. Burkhalter and T. Kaneko at Lattice97, Edinburg

    Finite-temperature chiral transitions in QCD with the Wilson quark action

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    We investigate the finite-temperature phase structure and the scaling of the chiral condensate in lattice QCD with two degenerate light quarks, using a renormalization group improved gauge action and the Wilson quark action. We obtain a phase diagram which is consistent with that from the parity-flavor breaking scenario. The scaling relation for the chiral condensate assuming the critical exponents and the scaling function of the three dimensional O(4) model is remarkably satisfied for a wide range of parameters. This indicates that the chiral transition in two flavor QCD is of second order in the continuum limit.Comment: LaTeX, 3 pages, 4 EPS figures, Talk presented at LATTICE97 (finite temperature
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