The Quark Number Susceptibility in Hard-Thermal-Loop Approximation

With the aid of the vector Ward-Takahashi identity we derive a general formula for the quark number susceptibility (QNS) which expresses the QNS as an integral expression only involving the full quark propagator at finite temperature and chemical potential. The QNS at finite temperature and zero chemical potential is calculated with the dressed quark propagator in the Hard-Thermal-Loop (HTL) approximation. A comparison of our result with the results of QNS in HTL approximation in previous literatures is given.