Abstract
We study the chemical potential effects on the chiral phase transition in a simply improved soft-wall AdS/QCD model, which can realize consistently the properties of linear confinement and spontaneous chiral symmetry breaking. The $\mu-T$ phase diagrams with both zero and physical quark masses have been obtained from this model. For the case of physical quark mass, the chiral transition has a crossover behavior at low chemical potential. With the increase of the chemical potential $\mu$, the critical temperature $T_c$ descends towards zero, and the crossover transition turns into a first-order one at some intermediate value of $\mu$, which implies that a critical end point naturally exists in this improved soft-wall model. All these features agree with our current perspective on the QCD phase diagram.
Highlights
The dynamics of quarks and gluons in quantum chromodynamics (QCD) has significant influence on the evolution of the universe and the existence of our world, which is intimately related to the two important features of QCD, i.e., the color confinement as a result of the nonlinear and nonperturbative dynamics of QCD and the mass generation originating from the quark condensate
We present the numerical results for the chiral transitions of σu and σs at four different chemical potentials μ 1⁄4 0; 0.35; 0.84; 1.2 GeV in Fig. 3, from which we find that the crossover transition at μ 1⁄4 0 will turn into a first-order one at large enough chemical potentials, and a second-order phase transition appears at some intermediate chemical potential, which signifies the existence of a critical endpoint (CEP), as expected from the general considerations of the μ − T phase diagram
The μ − T phase diagram obtained from our improved soft-wall model is shown in Fig. 6, where Tc as a function of μ has been given for both zero quark mass and physical quark mass, from which one can see that the transition temperature decreases with increasing chemical potential
Summary
The dynamics of quarks and gluons in quantum chromodynamics (QCD) has significant influence on the evolution of the universe and the existence of our world, which is intimately related to the two important features of QCD, i.e., the color confinement as a result of the nonlinear and nonperturbative dynamics of QCD and the mass generation originating from the quark condensate. Lattice QCD extrapolation to the finite chemical potential case is rather difficult due to the notorious sign problem and has so far not reached a consistent conclusion Other approaches such as the Dyson-Schwinger equation and the functional renormalization-group method [18,19,20,21,22] and effective models like the Polyakov-loop extended NambuJona-Lasinio model [23,24] have been used to address the relevant issues on QCD phase diagram. The temperature and chemical potential effects on the chiral condensate have been studied in the original softwall model [108] and in the modified versions [109,110], which cannot reproduce the basic structures of the QCD phase diagram. V, we give a summary of our work and discuss some issues on the chiral phase transition in this framework
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