Vector Meson Mass in Finite Density and Temperature Lattice QCD

Vector meson mass values are studied at finite chemical potential and temperature in lattice QCD with lattice size of 24 × 122× 6 using two flavors of staggered quarks. The investigation focuses on the change of the vector meson mass in the critical region close to T c with two different types of chemical potentials switched on: the isoscalar chemical potential μS and its isovector counterpart μV. It is found that the vector meson mass increases in the QGP phase with both chemical potentials and decreases with μS in the confinement phase.     

Chiral phase structure of the sixteen meson states in the SU(3) Polyakov linear-sigma model for finite temperature and chemical potential in a strong magnetic field

In characterizing the chiral phase-structure of pseudoscalar(J~(pc) = 0~(-+)), scalar(J~(pc) = 0~(++)), vector(J~(pc) =1~(--)) and axial-vector(J~(pc) = 1~(++)t) meson states and their dependence on temperature, chemical potential, and magnetic field,we utilize the SU(3) Polyakov linear-sigma model(PLSM) in the mean-field approximation. We first determine the chiral(non)strange quark condensates,σ_l and σ_s, and the corresponding deconfinement order parameters, φ and φ~*, in thermal and dense(finite chemical potential) medium and finite magnetic field. The temperature and the chemical potential characteristics of nonet meson states normalized to the lowest bosonic Matsubara frequency are analyzed. We note that all normalized meson masses become temperature independent at different critical temperatures. We observe that the chiral and deconfinement phase transitions are shifted to lower quasicritical temperatures with increasing chemical potential and magnetic field. Thus, we conclude that the magnetic field seems to have almost the same effect as the chemical potential, especially on accelerating the phase transition, i.e. inverse magnetic catalysis. We also find that increasing the chemical potential enhances the mass degeneracy of the various meson masses, while increasing the magnetic field seems to reduce the critical chemical potential, at which the chiral phase transition takes place. Our mass spectrum calculations agree well with the recent PDG compilations and PNJL, lattice QCD calculations, and QMD/UrQMD simulations.     

First and Second Sound Modes in a Uniform Fermi Gas

First and second sound modes in a uniform fermionic atom gas with Feshbaeh resonance are investigated in the frame of a two-fluid model at finite temperature. All thermodynamic quantities axe calculated for a given thermodynamic potential. The analytical results for thermodynamic quantities and sound velocities in BCS and BEC limits are obtained. The numerical results show that there exists a continuous interpolation for sound velocities of the first and second sound modes at fixed T/Tc between BCS and BEC limits. The existence of the second sound mode indicates the existence of superfluidity.     

Density Dependence of the Mass and Decay Constant of Pion in Nuclear Matter in the Dyson-Schwinger Equation Approach of QCD

With the Dyson-Schwinger equation formalism at finite chemical potential, we study the density dependence of the mass and decay constant of pion in nuclear matter. The calculated results indicate that both the mass and the decay constant remain almost constant at small chemical potential. As the chemical potential gets quite large, the decay constant increases and the mass decreases with the increasing of the chemical potential, and both of them vanish suddenly as a critical value is reached.     

Calculation of Quark-Number Susceptibility at Finite Chemical Potential and Temperature

We use the direct method proposed by He et al. [Phys. Lett. B 680 （2009） 432） to calculate the quark-number susceptibility （QNS） at finite temperature and the chemical potential in the quasi-particle model. In our approach the QNS is given by a formula solely involving the dressed quark propagator at finite chemical potential μ and temperature Τ. The QNS at finite μ and Τ is calculated in the quasi-particle model. It is found that at high temperatures the QNS tends to the ideal quark gas result. At very small temperatures the QNS vanishes. This vanishing behavior in the low-temperature region is consistent with the lattice results. For μ∈ [0,180] MeV, our results show that there exists a rapid increase of QNS near some temperatures. The temperature at which the rapid increase occurs shifts to smaller values with the increasing quark chemical potential. This rapid increase could be regarded as a signal of a crossover.     

Expanding the thermodynamical potential and analysis of the possible phase diagram of decon nement in the FL model

Decon nement phase transition is studied in the FL model at finite temperature and chemical potential. At MFT approximation, phase transition can only be first order in the whole μ-T phase plane. Using a Landau expansion, we further study the phase transition order and the possible phase diagram of decon nement. We discuss the possibilities of second order phase transitions in the FL model. From our analysis, if the cubic term in the Landau expansion could be cancelled by the higher order fluctuations, second order phase transition may occur. By an ansatz of the Landau parameters, we obtain a possible phase diagram with both the first and second order phase transitions, including the tri-critical point which is similar to that of the chiral phase transition.     

Expanding the thermodynamical potential and analysis of the possible phase diagram of deconfinement in the FL model

Deconfinement phase transition is studied in the FL model at finite temperature and chemical potential. At MFT approximation, phase transition can only be first order in the whole μ-T phase plane. Using a Landau expansion, we further study the phase transition order and the possible phase diagram of deconfinement. We discuss the possibilities of second order phase transitions in the FL model. From our analysis, if the cubic term in the Landau expansion could be cancelled by the higher order fluctuations, second order phase transition may occur. By an ansatz of the Landau parameters, we obtain a possible phase diagram with both the first and second order phase transitions, including the tri-critical point which is similar to that of the chiral phase transition.     

Calculation of Partition Function of QCD at Finite Chemical Potential

In equilibrium statistical field theory, the partition function has fundamental importance. In this paper we propose a direct and general method for calculating the partition function and equation of state of QCD at finite chemical potential. It is found that the partition function is totally determined by the dressed quark propagator at finite chemical potential up to a multiplicative constant. From this a criterion for the phase transition between the Nambu and the Wigner phases is obtained. This general method is applied to two specific cases： the free quark theory and QCD with a model dressed quark propagator having confinement features. In the first case, the standard Fermi distribution at T = 0 is reproduced. In the second case, we apply the conclusion in previous works to obtain the dressed quark propagator at finite chemical potential and find the unphysical result that the baryon number density vanishes for all values of chemical potential. The reason for this result is discussed.     

Effect of momentum anisotropy on quark matter in the quark-meson model

We investigate the chiral phase structure of quark matter with spheroidal momentum-space anisotropy specified by one anisotropy parameter ξ in the 2+1 flavor quark-meson model.We find that the chiral phase diagram and the location of the critical endpoint(CEP) are significantly affected by the value of ξ.With an increase inξ,the CEP is shifted to lower temperatures and higher quark chemical potentials.In addition,the temperature of the CEP is more sensitive to the anisotropy parameter than the corresponding quark chemical potential,which is the opposite to that from the finite system volume effect.The effects of the momentum anisotropy on the thermodynamic properties and scalar(pseudoscalar) meson masses are also studied at the vanishing quark chemical potential.The numerical results reveal that an increase in ξ can hinder the restoration of chiral symmetry.We also find that shear viscosity and electrical conductivity decrease as ξ increases.However,the bulk viscosity exhibits a significant nontrivial behavior with ξ in the entire temperature domain of interest.     

Nucleon Mass Splitting at Finite Isospin Chemical Potential

We investigate nucleon mass splitting at finite isospin chemical potential in the frame of the two-flavour Nambu-Jona-Lasinio model. It is analytically proven that in the phase with explicit isospin symmetry breaking, the proton mass decreases and the neutron mass increases linearly in the isospin chemical potential.