The XXV International Symposium on Lattice Field Theory

Physics Letters B, 1989

We present results of a numerical study of lattice QCD with four dynamical flavours of staggered fermions, performed by using a hybrid Monte Carlo algorithm on an 8× 123 lattice. We find a rapid change in the average value of the Polyakov loop at fie= 5.25 +_. 0.025 for a quark mass ma=0.025; at this mass value, the behaviour of the chiral order parameter, ( ~7~u), does not yet allow an independent determination of the transition point. Using existing hadron mass calculations, the value of Pc we have obtained here would lead to a transition temperature T~ 100 MeV.

Physical review, 1991

The long-standing issue of the nature of the critical line of lattice QCD with the Wilson quark action at finite temperatures, defined to be the line of vanishing pion screening mass, and its relation to the line of finite-temperature chiral transition is examined. Presented are both analytical and numerical evidence that the critical line forms a cusp at a finite gauge coupling, and that the line of chiral transition runs past the tip of the cusp without touching the critical line. Implications on the continuum limit and the flavor dependence of chiral transition are discussed.

Physical Review Letters, 2014

We report on the first lattice calculation of the QCD phase transition using chiral fermions at physical values of the quark masses. This calculation uses 2+1 quark flavors, spatial volumes between (4 fm) 3 and (11 fm) 3 and temperatures between 139 and 196 MeV . Each temperature was calculated using a single lattice spacing corresponding to a temporal Euclidean extent of Nt = 8. The disconnected chiral susceptibility, χ disc shows a pronounced peak whose position and height depend sensitively on the quark mass. We find no metastability in the region of the peak and a peak height which does not change when a 5 fm spatial extent is increased to 10 fm. Each result is strong evidence that the QCD "phase transition" is not first order but a continuous cross-over for mπ = 135 MeV. The peak location determines a pseudo-critical temperature Tc = 155(1)(8) MeV. Chiral SU (2)L ×SU (2)R symmetry is fully restored above 164 MeV, but anomalous U (1)A symmetry breaking is non-zero above Tc and vanishes as T is increased to 196 MeV.

2011

We discuss the universal critical behavior in (2+1)-flavor QCD by analyzing lattice data from improved staggered fermions generated by the HotQCD Collaboration. We present recent results from two different lattice discretizations and various lattice spacings (Ntau = 6,8,12) at fixed physical strange quark mass (ms) but varying light quark mass (ml). We find that the chiral order-parameter, i.e. the chiral condensate, shows the expected universal scaling that is associated with the critical point in the chiral limit already for light quark masses ml/ms<~0.05. From an analysis of the disconnected chiral susceptibility we estimate a preliminary value of the QCD transition temperature.

Physics Letters B, 2006

The transition temperature (T c ) of QCD is determined by Symanzik improved gauge and stout-link improved staggered fermionic lattice simulations. We use physical masses both for the light quarks (m ud ) and for the strange quark (m s ). Four sets of lattice spacings (N t =4,6,8 and 10) were used to carry out a continuum extrapolation. It turned out that only N t =6,8 and 10 can be used for a controlled extrapolation, N t =4 is out of the scaling region. Since the QCD transition is a non-singular cross-over there is no unique T c . Thus, different observables lead to different numerical T c values even in the continuum and thermodynamic limit. The peak of the renormalized chiral susceptibility predicts T c =151 MeV, wheres T c -s based on the strange quark number susceptibility and Polyakov loops result in 24(4) MeV and 25(4) MeV larger values, respectively. Another consequence of the cross-over is the non-vanishing width of the peaks even in the thermodynamic limit, which we also determine. These numbers are attempted to be the full result for the T =0 transition, though other lattice fermion formulations (e.g. Wilson) are needed to cross-check them.

Journal of High Energy Physics, 2010

The present paper concludes our investigations on the QCD cross-over transition temperatures with 2+1 staggered flavours and one-link stout improvement. We extend our previous two studies [Phys. Lett. B643 (2006) 46, JHEP 0906:088 (2009)] by choosing even finer lattices (N t =16) and we work again with physical quark masses. The new results on this broad cross-over are in complete agreement with our earlier ones. We compare our findings with the published results of the hotQCD collaboration. All these results are confronted with the predictions of the Hadron Resonance Gas model and Chiral Perturbation Theory for temperatures below the transition region. Our results can be reproduced by using the physical spectrum in these analytic calculations. The findings of the hotQCD collaboration can be recovered by using a distorted spectrum which takes into account lattice discretization artifacts and heavier than physical quark masses. This analysis provides a simple explanation for the observed discrepancy in the transition temperatures between our and the hotQCD collaborations.

Physics Letters B, 1984

Nuclear Physics B, 1993

The behaviour of the chiral condensate in QCD is investigated by means of a study of the distribution of the zeros of the partition function in the complex quark-mass plane. Simulations are performed at fixed temperature on three different spatial volumes at f3 = 5.04 and at fl = 4.9 and 13 = 5.2 on a 44 lattice. Evidence is found for a chirally related transition at non-zero quark mass in the intermediate coupling region for /3 <5.2 but superimposed upon a smooth behaviour for the condensate. The critical mass at which this transition is found in only weakly dependent on the spatial volume and decreases with decreasing temperature.

Quark Confinement and the Hadron Spectrum V, 2003

Results of the study of lattice QCD with two flavors of nonperturbatively improved Wilson fermions at finite temperature are presented. The transition temperature for mπ mρ ∼ 0.8 and lattice spacing a ∼ 0.12 fm is determined. A two-exponent ansatz is successfully applied to describe the heavy quark potential in the confinement phase. * Talk given by V. Bornyakov at "

2014

We determine the curvature of the (pseudo)critical line of QCD with n_f=2+1 staggered fermions at nonzero temperature and quark density, by analytic continuation from imaginary chemical potentials. Monte Carlo simulations are performed adopting the HISQ/tree action discretization, as implemented in the code by the MILC collaboration, suitably modified to include a nonzero imaginary baryon chemical potential. We work on a line of constant physics, as determined in Ref.Bazavov:2011nk, adjusting the couplings so as to keep the strange quark mass m_s fixed at its physical value, with a light to strange mass ratio m_l/m_s=1/20. In the present investigation we set the chemical potential at the same value for the three quark species, μ_l=μ_s≡μ. We explore lattices of different spatial extensions, 16^3× 6 and 24^3× 6, to check for finite size effects, and present results on a 32^3 × 8 lattice, to check for finite cut-off effects. We discuss our results for the curvature κ of the critical li...