Flavor dependent critical endpoint from holographic QCD through machine learning

A bstract QCD phase diagram in the T − μ plane and the equation of state for pure gluon, 2-flavor, 2+1-flavor systems, and 2+1+1-flavor systems have been investigated using the Einstein-Maxwell-Dilaton (EMD) framework at finite temperature and chemical potential. By inputting lattice QCD data for the equation of state and baryon number susceptibility at zero chemical potential into holographic model, all the parameters can be determined with the aid of machine learning algorithms. Our findings indicate that the deconfinement phase transition is of first order for the pure gluon system with critical temperature T c = 0.265 GeV at vanishing chemical potential. The phase transition for the 2-flavor, 2+1-flavor systems, and 2+1+1-flavor systems are crossover at vanishing chemical potential and first-order at high chemical potential, and the critical endpoint (CEP) in the T − μ plane locates at ( $$ {\mu}_B^c $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>μ</mml:mi> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> </mml:msubsup> </mml:math> = 0.46 GeV, T c = 0.147 GeV), ( $$ {\mu}_B^c $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>μ</mml:mi> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> </mml:msubsup> </mml:math> = 0.74 GeV, T c = 0.094 GeV), and ( $$ {\mu}_B^c $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>μ</mml:mi> <mml:mi>B</mml:mi> <mml:mi>c</mml:mi> </mml:msubsup> </mml:math> = 0.87 GeV, T c = 0.108 GeV), respectively. Additionally, the thermodynamic quantities of the system for different flavors at finite chemical potential are presented in this paper. It is observed that the difference between the 2+1-flavor and 2+1+1-flavor systems is invisible at vanishing chemical potential and low temperature. The location of CEP for 2+1+1-flavor system deviates explicitly from that of the 2+1-flavor system with the increase of chemical potential. Both 2+1-flavor and 2+1+1-flavor systems differ significantly from the 2-flavor system. Moreover, at zero temperature, the critical chemical potential is found to be μ B = 1.1 GeV, 1.6 GeV, 1.9 GeV for the 2-flavor, 2+1-flavor and 2+1+1-flavor systems, respectively.