Phase structure of two-color QCD at real and imaginary chemical potentials: Lattice simulations and model analyses

Abstract

We investigate the phase structure of two-color QCD at both real and imaginary chemical potentials (µ), performing lattice simulations and analyzing the data with the Polyakov-loop extended Nambu-Jona-Lasinio (PNJL) model. Lattice QCD simulations are done on an 8 3 × 4 lattice with the clover-improved two-flavor Wilson fermion action and the renormalization-group improved Iwasaki gauge action. We test the analytic continuation of physical quantities from imaginary µ to real µ by comparing lattice QCD results calculated at real µ with the result of analytic function the coefficients of which are determined from lattice QCD results at imaginary µ. We also test the validity of the PNJL model by comparing model results with lattice QCD ones. The PNJL model is good in the deconfinement region, but less accurate in the transition and confinement regions. This problem is improved by introducing the baryon degree of freedom to the model. It is also found that the vector-type four-quark interaction is necessary to explain lattice data on the quark number density.

Equation of state and transition temperatures in the quark-hadron hybrid model

“…It is also well-known that the QCD sum rule at finite density indicates the partial restoration of chiral symmetry in the normal nuclear matter [35]. Recently, it was also shown [36] that, in the LQCD simulations of the two-color QCD, the hadron effect is very important in reducing the absolute value of chiral condensate at finite temperature and finite density, when the system is in confined phase. Hence, it can be considered that the chiral condensate decreases even in the hadron phase, when the temperature increases.…”

Lattice simulation of $QC_2D$ with $N_f=2$ at non-zero baryon density

“…Especially interesting is to understand the effect of a non-zero baryon density on the breaking/recovery of the chiral symmetry. Similar investigations were performed in [3,5,6] for N f = 2 with Wilson fermions and in [7] [8] with N f = 4 and 8 flavors of staggered fermions respectively. However, Wilson fermions explicitly violate the chiral symmetry [9], thus they may not reveal all the phase transition lines in the QC 2 D phase diagram.…”

“…Therefore, we shall study a simpler theory: QFT with SU (2) gauge group and two degenerate flavors, where no sign problem arises [2,3,4], in order to better understand the qualitative features of the QCD phase diagram and to analyze the effect of a non-zero chemical potential on the properties of QGP. The point is that QC 2 D has specific relation for the Dirac operator [2,3]:…”

Gauge-invariant screening masses and static quark free energies in Nf=2+1 QCD at nonzero baryon density

“…In this case, the standard definition of electric and magnetic screening masses could be maintained; however, it is well known that for such special values of θ charge conjugation undergoes a spontaneous breaking above some critical temperature [55], which is usually known as the Roberge-Weiss transition temperature T RW and has been investigated in many lattice [56][57][58][59][60][61][62][63][64][65][66][67] and model [68][69][70][71][72][73][74][75][76][77][78][79] studies. For T > T RW , the spontaneous breaking induces a mixed electric-magnetic correlator, so one needs to extend the definition of the gauge-invariant screening masses as discussed above.…”