FINITE TEMPERATURE PHASE TRANSITION IN QCD WITH STRANGE QUARK: STUDY WITH WILSON FERMIONS ON THE LATTICE

The effect of the strange quark in the finite temperature phase transition of QCD is studied on the lattice. Using the one-plaquette gauge action and the Wilson quark action, the transition in the chiral limit is shown to be continuous for the case of degenerate two flavors, $N_F=2$, while it is of first order for $N_F \geq 3$. For a more realistic case of massless up and down quarks and a light strange quark, $N_F=2+1$, clear two state signals are observed both for $m_s \simeq 150$ and 400 MeV. In contrast to a previous result with staggered quarks, this suggests a first order transition in the real world. In order to see the implication of these results to the continuum limit, we started to study these issues using improved actions. First results using a RG improved gauge action combined with the standard Wilson quark is presented for the case of $N_F=2$: With this action the finite temperature transition is shown to be continuous in the chiral limit confirming the result of the standard action. Furthermore, not like the case of the standard action where lattice artifacts make the transition once very strong at intermediate values of the hopping parameter $K$ on $N_t=4$ and 6 lattices, a smooth crossover is found for the improved action when we increase $1/K-1/K_c$, in accord with a naive expectation about the fate of second order chiral transition at finite $m_q$.Comment: uuencoded compressed PS file, 9 pages, 10 figures, Talk given at the International Conference {\it Confinement95}, RCNP, Osaka, March 22-24, 199

An Introduction to Finite Temperature Quantum Chromodynamics on the Lattice

In these lectures, we introduce finite temperature QCD on the lattice to non-experts of the subject. We first formulate lattice QCD both at zero and finite temperatures. Then a section is devoted to the topic of improved lattice actions which are becoming an essential ingredient of precision studies of QCD on the lattice. We then discuss about finite temperature SU(3) gauge theory, i.e. QCD without dynamical quarks (quenched QCD). Finally, we report recent status of studies in full QCD taking into account the effects of dynamical quarks.Comment: Lectures presented at the 1997 Yukawa International Seminar (YKIS'97) on ``Non-Perturbative QCD --- Structure of the QCD Vacuum ---'', YITP, Kyoto, Japan, 2--12 Dec. 1997. To be published in the proceedings [Prog. Theor. Phys. Suppl.

Deconfining chiral transition in QCD on the lattice

The deconfining chiral transition in finite-temperature QCD is studied on the lattice using Wilson quarks. After discussing the nature of chiral limit with Wilson quarks, we first study the case of two degenerate quarks N_F=2, and find that the transition is smooth in the chiral limit on both N_t=4 and 6 lattices. For N_F=3, on the other hand, clear two state signals are observed for m_q \simm{<} 140 MeV on \nt=4 lattices. For a more realistic case of N_F=2+1, i.e.\ two degenerate u and d-quarks and a heavier s-quark, we study the cases m_s \simeq 150 and 400 MeV with m_u = m_d \simeq 0: In contrast to a previous result with staggered quarks, clear two state signals are observed for both cases, suggesting a first order QCD phase transition in the real world

Towards the QCD equation of state at the physical point using Wilson fermion

We study the (2+1)-flavor QCD at nonzero temperatures using nonperturbatively improved Wilson quarks of the physical masses by the fixed scale approach. We perform physical point simulations at finite temperatures with the coupling parameters which were adopted by the PACS-CS Collaboration in their studies using the reweighting technique. Zero temperature values are obtained on the PACS-CS configurations which are open to the public on the ILDG/JLDG. Finite temperature configurations are generated with the RHMC algorithm. The lattice sizes are $32^3 \times N_t$ with $N_t=14$, 13, $\cdots$, 4 which correspond to $T \approx 160$--550 MeV. We present results of some basic observables at these temperatures and the status of our calculation of the equation of state.Comment: 7 pages, 3 figures, proceedings of the 33rd International Symposium on Lattice Field Theory, July 14-18, 2015, Kobe, Japa

Quantum Chromodynamics with Many Flavors

We investigate the phase structure of lattice QCD for general number of flavors $N_F$. Based on numerical data combined with the results of the perturbation theory we propose the following picture: When $N_F \ge 17$, there is only one IR fixed point at vanishing gauge coupling, i.e., the theory in the continuum limit is trivial. On the other hand, when $16 \ge N_F \ge 7$, there is a non-trivial fixed point. 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 $N_F \le 6$.Comment: Talk presented by K. Kanaya at the 1997 Yukawa International Seminar (YKIS'97) on ``Non-Perturbative QCD --- Structure of the QCD Vacuum ---'', YITP, Kyoto, Japan, 2--12 Dec. 1997. To be published in the proceedings [Prog. Theor. Phys. Suppl.

Equation of state in 2+1 flavor QCD with improved Wilson quarks by the fixed scale approach

We study the equation of state in 2+1 flavor QCD with nonperturbatively improved Wilson quarks coupled with the RG-improved Iwasaki glue. We apply the $T$-integration method to nonperturbatively calculate the equation of state by the fixed-scale approach. With the fixed-scale approach, we can purely vary the temperature on a line of constant physics without changing the system size and renormalization constants. Unlike the conventional fixed-$N_t$ approach, it is easy to keep scaling violations small at low temperature in the fixed scale approach. We study 2+1 flavor QCD at light quark mass corresponding to $m_\pi/m_\rho \simeq 0.63$, while the strange quark mass is chosen around the physical point. Although the light quark masses are heavier than the physical values yet, our equation of state is roughly consistent with recent results with highly improved staggered quarks at large $N_t$.Comment: 14 pages, 12 figures, v2: Table I and Figure 3 are corrected, reference updated. Main discussions and conclusions are unchanged, v3: version to appear in PRD, v4: reference adde