Strange Quark Number Susceptibility Research Articles

QCD thermodynamics with continuum extrapolated Wilson fermions. II.

We continue our investigation of 2+1 flavor QCD thermodynamics using dynamical Wilson fermions in the fixed scale approach. Two additional pion masses, approximately 440 MeV and 285 MeV, are added to our previous work at 545 MeV. The simulations were performed at 3 or 4 lattice spacings at each pion mass. The renormalized chiral condensate, strange quark number susceptibility and Polyakov loop is obtained as a function of the temperature and we observe a decrease in the light chiral pseudo-critical temperature as the pion mass is lowered while the pseudo-critical temperature associated with the strange quark number susceptibility or the Polyakov loop is only mildly sensitive to the pion mass. These findings are in agreement with previous continuum results obtained in the staggered formulation.

The QCD phase diagram for external magnetic fields

The effect of an external (electro)magnetic field on the finite temperature transition of QCD is studied. We generate configurations at various values of the quantized magnetic flux with $N_f=2+1$ flavors of stout smeared staggered quarks, with physical masses. Thermodynamic observables including the chiral condensate and susceptibility, and the strange quark number susceptibility are measured as functions of the field strength. We perform the renormalization of the studied observables and extrapolate the results to the continuum limit using $N_t=6,8$ and 10 lattices. We also check for finite volume effects using various lattice volumes. We find from all of our observables that the transition temperature $T_c$ significantly decreases with increasing magnetic field. This is in conflict with various model calculations that predict an increasing $T_c(B)$. From a finite volume scaling analysis we find that the analytic crossover that is present at B=0 persists up to our largest magnetic fields $eB \approx 1 \textmd{GeV}^2$, and that the transition strength increases mildly up to this $eB\approx1 \textmd{GeV}^2$.

Chiral transition and deconfinement transition in QCD with the highly improved staggered quark (HISQ) action

We report preliminary results on the chiral and deconfinement aspects of the QCD transition at finite temperature using the Highly Improved Staggered Quark (HISQ) action on lattices with temporal extent of N τ = 6 and 8. The chiral aspects of the transition are studied in terms of quark condensates and the disconnected chiral susceptibility. We study the deconfinement transition in terms of the strange quark number susceptibility and the renormalized Polyakov loop. We find reasonably good agreement between our results and the recent continuum extrapolated results obtained with the stout staggered quark action.

Transition temperature and the equation of state from lattice QCD, Wuppertal–Budapest results

The QCD transition is studied on lattices up to Nt = 16. The chiral condensate is presented as a function of the temperature, and the corresponding transition temperature is extracted. The equation of state is determined on lattices with Nt = 6, 8, 10 and at some temperature values with Nt = 12. The pressure and the trace anomaly are presented as functions of the temperature in the range 100–1000 MeV. Using the same configurations, we determine the continuum extrapolated phase diagram of QCD on the μ–T plane for small to moderate chemical potentials. Two transition lines are defined with two quantities, the chiral condensate and the strange quark number susceptibility.

Transition temperature and the equation of state from lattice QCD, Wuppertal-Budapest results

The QCD transition is studied on lattices up to Nt = 16. The chiral condensate is presented as a function of the temperature, and the corresponding transition temperature is extracted. The equation of state is determined on lattices with Nt = 6,8,10 and at some temperature values with Nt = 12. The pressure and the trace anomaly are presented as functions of the temperature in the range 100 …1000 MeV . Using the same configurations we determine the continuum extrapolated phase diagram of QCD on the μ − T plane for small to moderate chemical potentials. Two transition lines are defined with two quantities, the chiral condensate and the strange quark number susceptibility.

The QCD phase diagram at nonzero quark density

We determine the phase diagram of QCD on the \mu-T plane for small to moderate chemical potentials. Two transition lines are defined with two quantities, the chiral condensate and the strange quark number susceptibility. The calculations are carried out on N_t =6,8 and 10 lattices generated with a Symanzik improved gauge and stout-link improved 2+1 flavor staggered fermion action using physical quark masses. After carrying out the continuum extrapolation we find that both quantities result in a similar curvature of the transition line. Furthermore, our results indicate that in leading order the width of the transition region remains essentially the same as the chemical potential is increased.

Transition temperature and the equation of state from lattice QCD, Wuppertal Budapest results

The QCD transition is studied on lattices up to Nt = 16. The chiral condensate is presented as a function of the temperature, and the corresponding transition temperature is extracted. The equation of state is determined on lattices with Nt = 6, 8, 10 and at some temperature values with Nt = 12. The pressure and the trace anomaly are presented as functions of the temperature in the range 100–1000 MeV. Using the same configurations, we determine the continuum extrapolated phase diagram of QCD on the μ–T plane for small to moderate chemical potentials. Two transition lines are defined with two quantities, the chiral condensate and the strange quark number susceptibility.

2+1flavor Polyakov–Nambu–Jona-Lasinio model at finite temperature and nonzero chemical potential

We extend the Polyakov-loop improved Nambu--Jona-Lasinio model to $2+1$ flavor case to study the chiral and deconfinement transitions of strongly interacting matter at finite temperature and nonzero chemical potential. The Polyakov loop, the chiral susceptibility of light quarks ($u$ and $d$), and the strange quark number susceptibility as functions of temperature at zero chemical potential are determined and compared with the recent results of lattice QCD simulations. We find that there is always an inflection point in the curve of strange quark number susceptibility accompanying the appearance of the deconfinement phase, which is consistent with the result of lattice QCD simulations. Predictions for the case at nonzero chemical potential and finite temperature are made as well. We give the phase diagram in terms of the chemical potential and temperature and find that the critical end point moves down to low temperature and finally disappears with the decrease of the strength of the 't Hooft flavor-mixing interaction.

The QCD transition temperature: Results with physical masses in the continuum limit

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 u d ) 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 ( 3 ) ( 3 ) 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.

Quark number susceptibilities, strangeness, and dynamical confinement

We report first results on the strange quark number susceptibility, chi_s, over a large range of temperatures, mainly in the plasma phase of QCD. Chi_s jumps across the phase transition temperature, T_c, and grows rapidly with temperature above but close to T_c. For all quark masses and susceptibilities in the entire temperature range studied, we found significant departures from ideal-gas values. We also observed a strong correlation between these quantities and the susceptibility in the scalar/pseudo-scalar channel, supporting ideas of ``dynamical confinement'' in the high temperature phase of the QCD plasma.