Running Coupling for Holographic QCD with Heavy and Light Quarks: Isotropic case

Abstract: We consider the running coupling constant in holographic models supported by Einstein-dilaton-Maxwell action for heavy and light quarks. To obtain the dependence of the running coupling constant $\alpha$ on temperature and chemical potential we impose boundary conditions on the dilaton field that depend on the position of the horizon. We use two types of boundary conditions: a simple boundary condition with the dilaton field vanishing at the horizon and a boundary condition that ensures an agreement with lattice calculations of string tension between quarks at zero chemical potential. The location of the 1st order phase transitions in $(\mu,T)$-plane does not depend on the dilaton boundary conditions for light and heavy quarks. At these phase transitions, the function $\alpha$ undergoes jumps depending on temperature and chemical potential. We also show that for the second boundary conditions the running coupling decreases with a temperature increase, and the dependence on temperature and chemical potential both for light and heavy quarks is actually specified in QGP phase by functions of one variable, demonstrating in this sense auto-model behavior.