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1. chinaXiv:201609.00076 [pdf]

Chiral Relaxation Time at the Chiral Crossover of Quantum Chromodynamics

M. Ruggieri; G. X. Peng; M. Chernodub
Subjects: Physics >> Nuclear Physics

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.

submitted time 2016-09-06 Hits812Downloads451 Comment 0

2. chinaXiv:201608.00215 [pdf]

Quark matter in a parallel electric and magnetic field background: Chiral phase transition and equilibration of chiral density

M. Ruggieri; G. X. Peng
Subjects: Physics >> Nuclear Physics

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.

submitted time 2016-08-31 Hits917Downloads438 Comment 0

3. chinaXiv:201608.00207 [pdf]

Critical Temperature of Chiral Symmetry Restoration for Quark Matter with a Chiral Chemical Potential

M. Ruggieri; G. X. Peng
Subjects: Physics >> Nuclear Physics

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 nonlocal Nambu-Jona-Lasinio model. This model allows to introduce in the simplest way possible a Euclidean momentum,?pE, dependent quark mass function which decays (neglecting logarithms) as?1/p2E?for large?pE, in agreement with asymptotic behaviour expected in QCD in presence of a nonperturbative quark condensate. We focus on the critical temperature for chiral symmetry restoration in the chiral limit,?Tc, versus?μ5, as well as on the order of the phase transition. We find that?Tc?increases with?μ5, and that the transition remains of the second order for the whole range of?μ5?considered.

submitted time 2016-08-31 Hits728Downloads317 Comment 0

4. chinaXiv:201608.00199 [pdf]

Critical Temperature of Chiral Symmetry Restoration for Quark Matter with a Chiral Chemical Potential

M. Ruggieri; G. X. Peng
Subjects: Physics >> Nuclear Physics

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.

submitted time 2016-08-30 Hits781Downloads416 Comment 0

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