Lü Xiao-Fu

Calculation of four-quark condensate beyond vacuum saturation approximation

Based on a modification of the global color symmetry model, we have calculated the four-quark condensate [: (q) over bar gamma mu lambdaC degrees /2 q(q) over bar gamma mu lambdaC degrees /2 q :] beyond vacuum saturation approximation by including the contribution of pi and sigma masons. The numerical results show that there is a sizeable correction of the four-quark condensate in comparison with its factorized value using the vacuum saturation approximation.

Neutron star magnetic field as for nonzero photon mass

We investigate the neutron star magnetic field by the relative mean-field theory, where the photon effective mass depending on baryon density of charged particles is nonzero. This field is produced by star itself, which is the function of baryon density. The result fits the observations.

The Mixed Quark-Gluon Condensate from the Global Color Symmetry Model*

The mixed quark-gluon condensate from the global color symmetry model is derived. It is shown that the mixed quark-gluon condensate depends explicitly on the gluon propagator. This interesting feature may be regarded as an additional constraint on the model of gluon propagator. The values of the mixed quark-gluon condensate from some ansatz for the gluon propagator are compared with those determined from QCD sum rules.

Some properties of pi meson in nuclear matter with finite density

In the GCM we study some properties of pi meson as the Goldstone bosons in a nuclear matter with finite density. Using the effective action in a nuclear matter, we calculate the decay constant and pi mass as functions of the chemical potential. The relation between the chemical potential and the density of a nuclear matter is firstly given here. We find that f(pi) and m(pi) monotonously decrease as nuclear matter density increases. The result is consistent with the usual assumption that the chiral symmetry is gradually restored as the density of a nuclear matter increases.

Effect of a Small Current Quark Mass on Dressed Gluon and Quark Propagator

Based on the Dyson–Schwinger approach, a method for obtaining the small current quark mass effect on the dressed gluon and quark propagator is developed. A comparison with the results of the previous approach is given.

Nonlocal four-quark condensate and vacuum susceptibilities

Based on the quark propagator in the instanton dilute liquid approximation, we have determined the nonlocal four-quark condensate at the mean-field level in the framework of global color symmetry model. By making use of this formula, the vacuum susceptibility (pion susceptibility) was calculated in this paper. The theoretical analysis and numerical calculation show that even at the mean-field level the naive vacuum saturation approximation is not a good approximation when we consider nonlocal four-quark condensate.

Influence of Quark Current Mass on Quark Condensate at Finite Temperature

Using the Dyson—Schwinger equation and perturbation theory, we define the quark condensate with the quark current mass at finite temperature, and compare the quark condensate at finite temperature for the quark current mass m = 0 and m ≠ 0, respectively. The results show that the two-quark condensates have significantly different behaviors from the quark condensate in the chiral limit, and the quark current mass has a very important influence over the solution of the non-perturbative term.

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

Revisiting Chiral Extrapolation by Studying a Lattice Quark Propagator

The quark propagator in the Landau gauge is studied on the lattice, including the quenched and the unquenched results. No obvious unquenched effects are found by comparing the quenched quark propagator with the dynamical one. For the quenched and unquenched configurations, the results with different quark masses have been computed. For the quark mass function, a nonlinear chiral extrapolating behavior is found in the infrared region for both the quenched and dynamical results.

Nucleon internal structure: a new set of quark, gluon momentum, angular momentum operators and parton distribution functions

It is unavoidable to deal with the quark and gluon momentum and angular momentum contributions to the nucleon momentum and spin in the study of nucleon internal structure. However we never have the quark and gluon momentum, orbital angular momentum and gluon spin operators which satisfy both the gauge invariance and the canonical momentum and angular momentum commutation relation. The conflicts between the gauge invariance and 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 the gauge invariance and canonical momentum and angular momentum commutation relation, are proposed. The key point to achieve such a proper decomposition 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.