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Register a new userEquation of state in finite-temperature QCD with two flavors of improved Wilson quarks
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We present results of a first study of equation of state in finite-temperature QCD with two flavors of Wilson-type quarks. Simulations are made on lattices with temporal size $N_t=4$ and 6, using an RG-improved action for the gluon sector and a meanfield-improved clover action for the quark sector. The lines of constant physics corresponding to fixed values of the ratio $m_{rm PS}/m_{rm V}$ of the pseudo-scalar to vector meson masses at zero temperature are determined, and the beta functions which describe the renormalization-group flow along these lines are calculated. Using these results, the energy density and the pressure are calculated as functions of temperature along the lines of constant physics in the range $m_{rm PS}/m_{rm V} = 0.65$--0.95. The quark mass dependence in the equation of state is found to be small for $m_{rm PS}/m_{rm V} simlt 0.8$. Comparison of results for $N_t=4$ and $N_t=6$ lattices show significant scaling violation present in the $N_t=4$ results. At high temperatures the results for $N_t=6$ are quite close to the continuum Stefan-Boltzmann limit, suggesting the possibility of a precise continuum extrapolation of thermodynamic quantities from simulations at $N_tsimgt 6$.
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We study the equation of state in two-flavor QCD at finite temperature and density. Simulations are made with the RG-improved gluon action and the clover-improved Wilson quark action. Along the lines of constant physics for $m_{rm PS}/m_{rm V} = 0.65$ and 0.80, we compute the derivatives of the quark determinant with respect to the quark chemical potential $mu_q$ up to the fourth order at $mu_q=0$. We adopt several improvement techniques in the evaluation. We study thermodynamic quantities and quark number susceptibilities at finite $mu_q$ using these derivatives. We find enhancement of the quark number susceptibility at finite $mu_q$, in accordance with previous observations using staggered-type quarks. This suggests the existence of a nearby critical point.
We report results for the interaction measure, pressure and energy density for nonzero temperature QCD with 2+1 flavors of improved staggered quarks. In our simulations we use a Symanzik improved gauge action and the Asqtad $O(a^2)$ improved staggered quark action for lattices with temporal extent $N_t=4$ and 6. The heavy quark mass $m_s$ is fixed at approximately the physical strange quark mass and the two degenerate light quarks have masses $m_{ud}approx0.1 m_s$ or $0.2 m_s$. The calculation of the thermodynamic observables employs the integral method where energy density and pressure are obtained by integration over the interaction measure.
We present an update of our study of high temperature QCD with three flavors of quarks, using a Symanzik improved gauge action and the Asqtad staggered quark action. Simulations are being carried out on lattices with Nt=4, 6 and 8 for the case of three degenerate quarks with masses less than or equal to the strange quark mass, $m_s$, and on lattices with Nt=6 and 8 for degenerate up and down quarks with masses in the range 0.2 m_s leq m_{u,d} leq 0.6 m_s, and the strange quark fixed near its physical value. We also report on first computations of quark number susceptibilities with the Asqtad action. These susceptibilities are of interest because they can be related to event-by-event fluctuations in heavy ion collision experiments. Use of the improved quark action leads to a substantial reduction in lattice artifacts. This can be seen already for free fermions and carries over into our results for QCD.
We present results obtained in QCD with two flavors of non-perturbatively improved Wilson fermions at finite temperature on $16^3 times 8$ and $24^3 times 10$ lattices. We determine the transition temperature in the range of quark masses $0.6<m_pi/m_rho<0.8$ at lattice spacing a$approx$0.1 fm and extrapolate the transition temperature to the continuum and to the chiral limits. We also discuss the order of phase transition.
We study the curvature of the chiral transition/crossover line between the low-temperature hadronic phase and the high-temperature quark-gluon-plasma phase at low densities, performing simulations of two-flavor QCD with improved Wilson quarks. After confirming that the chiral order parameter defined by a Ward-Takahashi identity is consistent with the scaling of the O(4) universality class at zero chemical potential, we extend the scaling analysis to finite chemical potential to determine the curvature of the chiral transition/crossover line at low densities assuming the O(4) universality. To convert the curvature in lattice units to that of the $T_c(mu_B)$ in physical units, we evaluate the lattice scale applying a gradient flow method. We find $kappa=0.0006(1)$ in the chiral limit, which is much smaller than that obtained in (2+1)-flavor QCD with improved staggered quarks.
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