Universality driven analytic structure of QCD crossover: radius of convergence and QCD critical point

Abstract

Recent lattice QCD calculations show strong indications that the crossover of QCD at zero baryon chemical potential (μB) is a remnant of the second order chiral phase transition. The non-universal parameters needed to map temperature T and μB to the universal properties of the second order chiral phase transition were determined by lattice QCD calculations. Motivated by these advances, first, we discuss the analytic structure of the partition function – the so-called Yang-Lee edge singularity – in the QCD crossover regime, solely based on universal properties. Then, utilizing the lattice calculated non-universal parameters, we map this singularity to the real T and complex μB plane, in order to find the radius of convergence for a Taylor series expansion of QCD partition function around μB = 0 in the QCD crossover regime. Our most important findings are: (i) An universality-based estimate of the radius of convergence around μB = 0; (ii) Universality and lattice QCD based constraints on the location of the QCD critical point in the T −μB plane.