Study on the character of elementary excitations around critical point of QCD phase transitions

点击翻译按钮获取中文摘要

We have shown that the quarks around the chiral transition at finite temperature can change their quasi-particle picture owing to the coupling to the chiral soft modes. Around the critical point, there may appear soft modes which are coupled to the fluctuations of the order parameter of the phase transition. We have investigated the quark self-energy due to this bosonic mode at finite temperature. We have shown that the spectral function of the quark gets to have three peaks in the low-energy region : The two of them existing in the positive-and negative-energy regions correspond to the normal-quark and plasmino excitations familiar in the hard-thermal loop approximation valid in the extremely high-temperature region. We have shown that there appears an additional excitation with a vanishingly small energy. We have clarified the mechanism for the formation of such a multiple peak structure in terms of the level crossing between the quark and the thermally excited anti-quarks. We have also shown that such a realization of the three-peak structure does not depend on the type of the bosonic excitation, i.e., it may be vector or axial vector type. We have also identified the poles corresponding to the three peaks, and examined the temperature dependence of the poles. We have found that the set of the three trajectories changes its structure in a drastic way when the quak mass is raised.We have tried to construct sensible hydrodynamic equations for viscous fluids using the so called renormalization-group method. We have shown that the obtained equation in the particle fame does not show a pathological behavior unlike to the original Eckart equation.