We present a modified version of quark mass scaling via considering the important one-gluonexchange interaction between quarks in the quark mass density-dependent model. The properties of strange quark matter and the structure of strange stars are then studied with the new scaling and a self-consistent thermodynamic treatment. It is found that the one-gluon-exchange effect lowers the system energy considerably, makes the equation of state stiffer, and the sound velocity tends to the ultra-relativistic value faster, which make the biggest value of the maximum mass of strange stars become as big as approximately 2 times the solar mass, in accordance with the latest astronomical observations.
We investigate the properties of strange quark matter （SQM） in a strong magnetic field with quark confinement by the density dependence of quark masses considering the total baryon number conservation, charge neutrality and chemical equilibrium. It is found that an additional term should appear in the pressure expression to maintain thermodynamic consistency. At fixed density, the energy density of magnetized SQM varies with the magnetic field strength. By increasing the field strength an energy minimum exists located at about 6×10^19 Gauss when the density is fixed at two times the normal nuclear saturation density.
The properties of strange quark matter and the structures of(proto-)strange stars are studied within the framework of a baryon density-dependent quark mass model,where a novel quark mass scaling and self-consistent thermodynamic treatment are adopted.Our results indicate that the perturbative interaction has a significant impact on the properties of strange quark matter.It is determined that the energy per baryon increases with temperature,while the free energy decreases and eventually becomes negative.At fixed temperatures,the pressure at the minimum free energy per baryon is zero,suggesting that the thermodynamic self-consistency is preserved.Furthermore,the sound velocity v in quark matter approaches the extreme relativistic limit(c/√3)as the density increases.By increasing the strengths of the confinement parameter D and perturbation parameter C,the tendency for v to approach the extreme relativistic limit at high density is slightly weakened.For(proto-)strange stars,the novel quark mass scaling can accommodate massive proto-strange stars with their maximum mass surpassing twice the solar mass by considering the isentropic stages along the star evolution line,where the entropy per baryon of the star matter is set to be 0.5 and 1 with the lepton fraction Y_(l)=0.4.
Starting from the Kubo formula and the QCD low energy theorem, we study the the bulk viscosity of hot dense quark matter in the PNJL model from the equation of state. We show that the bulk viscosity has a sharp peak near the chiral phase transition, and that the ratio of bulk viscosity over entropy rises dramatically in the vicinity of the phase transition. These results agree with those from the lattice and other model calculations. In addition, we show that the increase of chemical potential raises the bulk viscosity.
Within the nonlinear relativistic mean field(NLRMF) model, we show that both the pressure of symmetric nuclear matter at supra-saturation densities and the maximum mass of neutron stars are sensitive to the skewness coefficient, J_0, of symmetric nuclear matter. Using experimental constraints on the pressure of symmetric nuclear matter at supra-saturation densities from flow data in heavy-ion collisions and the astrophysical observation of a large mass neutron star PSR J0348+0432, with the former favoring a smaller J_0 while the latter favors a larger J_0, we extract a constraint of -494 MeV≤J_0≤-10 MeV based on the NL-RMF model. This constraint is compared with the results obtained in other analyses.
The properties of strange star matter are studied in the equivparticle model with inclusion of non-Newtonian gravity. It is found that the inclusion of non-Newtonian gravity makes the equation of state stiffer if Witten＇s conjecture is true. Correspondingly, the maximum mass of strange stars becomes as large as two times the solar mass, and the maximum radius also becomes bigger. The coupling to boson mass ratio has been constrained within the stability range of strange quark matter.
