分类： 物理学 >> 核物理学 提交时间： 2016-09-19
摘要： We investigate the chiral phase transition in the soft-wall model of AdS/QCD at zero chemical potential for two-flavor and three-flavor cases, respectively. We show that there is no spontaneous chiral symmetry breaking in the original soft-wall model. After detailed analysis, we find that in order to realize chiral symmetry breaking and restoration, both profiles for the scalar potential and the dilaton field are essential. The scalar potential determines the possible solution structure of the chiral condensate, except the mass term, it takes another quartic term for the two-flavor case, and for the three-flavor case, one has to take into account an extra cubic term due to the t'Hooft determinant interaction. The profile of the dilaton field reflects the gluodynamics, which is negative at a certain ultraviolet scale and approaches positive quadratic behavior at far infrared region. With this set-up, the spontaneous chiral symmetry breaking in the vacuum and its restoration at finite temperature can be realized perfectly. In the two-flavor case, it gives a second order chiral phase transition in the chiral limit, while the transition turns to be a crossover for any finite quark mass. In the case of three-flavor, the phase transition becomes a first order one in the chiral limit, while above sufficient large quark mass it turns to be a crossover again. This scenario agrees exactly with the current understanding on chiral phase transition from lattice QCD and other effective model studies.
分类： 物理学 >> 核物理学 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： The relation between the vector-isoscalar and vector-isovector interactions in the two-flavor Nambu-Jona-Lasinio (NJL) model is investigated under the different constraints from QCD. We demonstrate that the flavor-mixing can be induced by the mismatched vector-isoscalar and vector-isovector interactions at finite baryon chemical potential and isospin chemical potential I. The effect of this non-anomaly flavor-mixing on the possible separate chiral transitions at nonzero I is studied under the assumption of the effective restoration of U(1)A symmetry. We find that for the weak isospin asymmetry, the two separate phase boundaries found previously can be converted into one only if the vector-isovector coupling gvv is significantly stronger than the vector-isoscalar one gvs without the axial anomaly.
分类： 物理学 >> 核物理学 提交时间： 2016-08-31
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 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.
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 提交时间： 2016-05-08
摘要： Based on the universal properties of a critical point in different systems and that the QCD phase transitions fall into the same universality classes as the 3-dimensional Ising, O(2) or O(4) spin models, the critical behavior of cumulants and higher cumulant ratios of the order parameter from the three kinds of spin models is studied. We found that all higher cumulant ratios change dramatically the sign near the critical temperature. The qualitative critical behavior of the same order cumulant ratio is consistent in these three models.
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.
点击量
待评议
点击量
下载量
评论
通过
