分类： 物理学 >> 核物理学 提交时间： 2016-09-06
摘要： We study microscopic processes responsible for chirality flips in the thermal bath of Quantum Chromodynamics at finite temperature and zero baryon chemical potential. We focus on the temperature range where the crossover from chirally broken phase to quark-gluon plasma takes place, namely T≃(150,200) MeV. The processes we consider are quark-quark scatterings mediated by collective excitations with the quantum number of pions and σ-meson, hence we refer to these processes simply as \sugg{to} one-pion (one-σ) exchange\sugg{s}. We use a Nambu-Jona-Lasinio model to compute equilibrium properties of the thermal bath, as well as the relevant scattering kernel to be used in the collision integral to estimate the chiral relaxation time τ. We find τ≃0.1÷1 fm/c around the chiral crossover.
分类： 物理学 >> 核物理学 提交时间： 2016-08-31
摘要： In this article we study spontaneous chiral symmetry breaking for quark matter in the background of static and homogeneous parallel electric field $\bm E$ and magnetic field $\bm B$. We use a Nambu-Jona-Lasinio model with a local kernel interaction to compute the relevant quantities to describe chiral symmetry breaking at finite temperature for a wide range of E and B. We study the effect of this background on inverse catalysis of chiral symmetry breaking for E and B of the same order of magnitude. We then focus on the effect of equilibration of chiral density, n5, produced dynamically by axial anomaly on the critical temperature. The equilibration of n5, a consequence of chirality flipping processes in the thermal bath, allows for the introduction of the chiral chemical potential, μ5, which is computed self-consistently as a function of temperature and field strength by coupling the number equation to the gap equation, and solving the two within an expansion in E/T2, B/T2 and μ25/T2. We find that even if chirality is produced and equilibrates within a relaxation time τM, it does not change drastically the thermodynamics, with particular reference to the inverse catalysis induced by the external fields, as long as the average μ5 at equilibrium is not too large.
分类： 物理学 >> 核物理学 提交时间： 2016-08-30
摘要： In this article we study restoration of chiral symmetry at finite temperature for quark matter with a chiral chemical potential, μ5, by means of a quark-meson model with vacuum fluctuations included. Vacuum fluctuations give a divergent contribution to the vacuum energy, so the latter has to be renormalized before computing physical quantities. The vacuum term is important for restoration of chiral symmetry at finite temperature and μ5≠0, therefore we present several plausible renormalization schemes for the ultraviolet divergences at μ5≠0. Then we compute the critical temperature as a function of μ5. The main result of our study is that the choice of a renormalization scheme affects the critical temperature; among the three renormalization schemes we investigate, there exists one in which the critical temperature increases with μ5, a result which has not been found before by chiral model studies and which is in qualitative agreement with recent lattice data as well as with studies based on Schwinger-Dyson equations and universality arguments.
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