Sun Wei-Min

Quark number susceptibility around the critical end point

The quark number susceptibility is expressed as an integral in terms of dressed quark propagator and dressed vector vertex. It is then investigated with the latter two- and three-point functions confronted with a Dyson-Schwinger equation model which accommodates both finite temperature and baryon chemical potential. The critical end point in the phase diagram is identified and the behavior of the quark number susceptibility around the critical end point is highlighted. The qualitative features found agree with recent lattice QCD simulation results.

Critical Mass of Gauge Boson in Rainbow QED3

In three-dimensional quantum electrodynamics (QED3) with a massive gauge boson, we investigate the coupled Dyson–Schwinger equations for the fermion and photon propagators in the rainbow approximation, and obtain the critical gauge boson mass for various numbers of the fermion flavors. A comparision with the previous results is presented.

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 T. The QNS at finite μ and T 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.

The Quark Number Susceptibility of QCD at Finite Temperature and Chemical Potential

We calculate the quark number density and quark number susceptibility (QNS) of QCD at finite chemical potential mu and finite temperature T in the framework of a new nonperturbative QCD model. Analysis and discussions of the calculated results of the QNS are given. It is found that the quark number density has a singularity when mu comes close to a critical value mu(0), and the QNS chi(mu, T) becomes discontinuous at some values of T. At high temperature the QNS approaches the free quark gas result, while at very low temperature the QNS equals zero. Importantly, the QNS shows a sudden increase near some temperature (T similar to 120MeV), which may be regarded as the signal of a crossover.

Quark Stars Investigated using an Improved Quasi-Particle Model

The equation of state (EOS) of cold and dense strongly interacting matter is crucial for better research of compact stars, i.e., neutron stars and quark stars. We generalize our improved quasi-particle model from finite temperature and zero chemical potential [Phys. Lett. B 711 (2012) 65] to the case of zero temperature and finite chemical potential to obtain an EOS of our improved quasi-particle model and then apply this EOS to study the structure of a quark star. The results are consistent with the most recent astronomical observational data.

Wigner solution to the quark gap equation in the nonzero current quark mass

From the graphical representation of the Dyson—Schwinger equation for the dressed gluon propagator it is shown that the gluon propagator in the Wigner phase should be different from that in the Nambu phase. Based on this analysis, we propose a modified gluon propagator to reflect this fact. With such a modified gluon propagator, in the framework of the Nambu—Jona—Lasinio (NJL) model, we obtain the Wigner solution to the quark gap equation at finite current quark mass, which has not been found in literature. This provides a new point of view to study partial restoration of chiral symmetry at finite temperature and chemical potential.

An Improved Quasi-particle Model Framework for Quark-Gluon Plasma from the Path Integral Formalism

An improved framework for the quasi-particle model is presented. Unlike the previous approach of establishing the quasi-particle model, we introduce a classical background field (it is allowed to depend on temperature) to deal with the infinity of thermal vacuum energy which exists in previous quasi-particle models. After taking into account the effect of this classical background field, the partition function of the quasi-particle system can be well defined. Based on this and following the standard ensemble theory, we construct a thermodynamically consistent quasi-particle model without the need to reformulate the statistical mechanics or the thermodynamic consistency relation. It is shown that our method is general and can be generalized to the case in which the effective mass depends not only on the temperature but also on the chemical potential.

Modified Approach for Calculating Four-Quark Condensates

By differentiating the dressed quark propagator with respect to a variable background field, the linear response of the dressed quark propagator in the presence of the background field can be obtained. From this general method, using the vector background field as an illustration, we extract a general formula for the four-quark condensate |:(0)γμq(0)(0)γμq(0):|. This formula contains the corresponding fully dressed vector vertex. We use this formula to analyze the factorization problem of the four-quark condensate and show that in the bare vertex approximation factorization holds exactly.

Susceptibilities of QCD Vacuum from Renormalized Dyson–Schwinger Equations*

The pion and tensor vacuum susceptibilities are calculated in the framework of the renormalizable Dyson–Schwinger equations. A comparison with the results of other nonperturbative QCD approaches is given.

Gauge invariance and quantization applied to atom and nucleon internal structure

The prevailing theoretical quark and gluon momentum, orbital angular momentum and spin operators, satisfy either gauge invariance or the corresponding canonical commutation relation, but one never has these operators which satisfy both except the quark spin The conflicts between gauge invariance and the canonical quantization requirement, of these operators are discussed A new set of quark and gluon momentum, orbital angular momentum and spin operators, which satisfy both gauge invariance and canonical momentum and angular momentum commutation relation, are proposed To achieve such a proper decomposition the key point is to separate the gauge field into the pure gauge and the gauge covariant parts The same conflicts also exist in QED and quantum mechanics, and have been solved in the same manner The impacts of this new decomposition to the nucleon internal structure are discussed