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Register a new userQCD thermodynamics at zero and non-zero density
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We present results on the QCD equation of state, obtained with two different improved dynamical staggered fermion actions and almost physical quark masses. Lattice cut-off effects are discussed in detail as results for three different lattice spacings are available now, i.e. results have been obtained on lattices with temporal extent of $N_tau=4,6$ and 8. Furthermore we discuss the Taylor expansion approach to non-zero baryon chemical potential by means of an expansion of the pressure. We use the expansion coefficients to calculate various fluctuations and correlations among hadronic charges. We find that the correlations reproduce the qualitative behavior of the resonance gas model below $T_c$ and start to agree with the free gas predictions for $Tgsim 1.5T_c$.
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We present results for pseudo-critical temperatures of QCD chiral crossovers at zero and non-zero values of baryon ($B$), strangeness ($S$), electric charge ($Q$), and isospin ($I$) chemical potentials $mu_{X=B,Q,S,I}$. The results were obtained using lattice QCD calculations carried out with two degenerate up and down dynamical quarks and a dynamical strange quark, with quark masses corresponding to physical values of pion and kaon masses in the continuum limit. By parameterizing pseudo-critical temperatures as $ T_c(mu_X) = T_c(0) left[ 1 -kappa_2^{X}(mu_{X}/T_c(0))^2 -kappa_4^{X}(mu_{X}/T_c(0))^4 right] $, we determined $kappa_2^X$ and $kappa_4^X$ from Taylor expansions of chiral observables in $mu_X$. We obtained a precise result for $T_c(0)=(156.5pm1.5);mathrm{MeV}$. For analogous thermal conditions at the chemical freeze-out of relativistic heavy-ion collisions, i.e., $mu_{S}(T,mu_{B})$ and $mu_{Q}(T,mu_{B})$ fixed from strangeness-neutrality and isospin-imbalance, we found $kappa_2^B=0.012(4)$ and $kappa_4^B=0.000(4)$. For $mu_{B}lesssim300;mathrm{MeV}$, the chemical freeze-out takes place in the vicinity of the QCD phase boundary, which coincides with the lines of constant energy density of $0.42(6);mathrm{GeV/fm}^3$ and constant entropy density of $3.7(5);mathrm{fm}^{-3}$.
A status of lattice QCD thermodynamics, as of 2013, is summarized. Only bulk thermodynamics is considered. There is a separate section on magnetic fields.
The WHOT-QCD Collaboration is pushing forward lattice studies of QCD at finite temperatures and densities using improved Wilson quarks. We first present results on QCD at zero and finite densities with two flavors of degenerate quarks (N_F=2 QCD) adopting the conventional fixed-Nt approach. We then report on the status of a study of N_F=2+1 QCD adopting a fixed-scale approach armed with the T-integration method which we have developed.
The WHOT-QCD Collaboration is pushing forward a series of lattice studies of QCD at finite temperatures and densities using improved Wilson quarks. Because Wilson-type quarks require more computational resources than the more widely adopted staggered-type quarks, various theoretical and computational techniques have to be developed and applied. In this paper, we introduce the fixed-scale approach armed with the T-integration method, the Gaussian method based on the cumulant expansion, and the histogram method combined with the reweighting technique. Adopting these methods, we have carried out the first study of finite-density QCD with Wilson-type quarks and the first calculation of the equation of state with 2+1 flavors of Wilson-type quarks. We present results of these studies and discuss perspectives towards a clarification of the properties of 2+1 flavor QCD at the physical point, at finite temperatures and densities.
We present details of a lattice QCD calculation of the $B_sto D_s^*$ axial form factor at zero recoil using the Highly Improved Staggered Quark (HISQ) formalism on the second generation MILC gluon ensembles that include up, down, strange and charm quarks in the sea. Using the HISQ action for all valence quarks means that the lattice axial vector current that couples to the $W$ can be renormalized fully non-perturbatively, giving a result free of the perturbative matching errors that previous lattice QCD calculations have had. We calculate correlation functions at three values of the lattice spacing, and multiple `$b$-quark masses, for physical $c$ and $s$. The functional dependence on the $b$-quark mass can be determined and compared to Heavy Quark Effective Theory expectations, and a result for the form factor obtained at the physical value of the $b$-quark mass. We find $mathcal{F}^{B_sto D_s^*}(1) = h^s_{A_1}(1) = 0.9020(96)_{text{stat}}(90)_{text{sys}}$. This is in agreement with earlier lattice QCD results, which use NRQCD $b$ quarks, with a total uncertainty reduced by more than a factor of two. We discuss implications of this result for the $Bto D^*$ axial form factor at zero recoil and for determinations of $V_{cb}$.
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