Calculation Of Quark Condensate In Nuclear Matter By Using The Chiral Symmetry Spontaneous Breaking Lagrangian

QCD has a non-trivial vacuum with non-perturbation condensates of quarks and gluons. As all known, in the low energy region, QCD has two very important properties: chiral symmetry spontaneous breaking and confinement. It is believed that the two properties are closely related to the vacuum characteristics. By combining the global color symmetry model (GCM) of QCD and the instanton dilute liquid approximation we have investigated the vacuum properties and some results which fit experimental data quite well have been obtained. The investigations show that the chiral symmetry spontaneous breaking is the key to understand the low energy feature of the strongly interacting physics. The chiral symmetry spontaneous breaking can be characterized by the quark condensates .In the QCD sum rule approach the condensates are introduced phenomenogically in the theory and their values are determined by fitting experimental data. Many evidences shows that the chiral symmetry spontaneou breaking appears below the scale 1 Gev. Meanwhile, one believes that the evolution from chiral symmetry to the spontaneous breaking is of second order phase transition. Thus the quark condensates in the nuclear matter decreases gradualy as the density of the nuclear matter increases.Using the chiral symmetry spontaneous breaking Lagrangian with mean-field approxiation we investigate the in-medium quark condensate < qq >.It is found that the condensate decreases with the nuclear matter density/? ,meanwhile, the descent deviates from the linear decrease and becomes remarkably slow as the density of the nuclear matter further increases. It shows that the chiral symmetry spontaneous breaking is only partially restored in nuclear matter.