The Universal Equation of State near the Critical Point of QCD

TL;DR

This paper derives the universal equation of state near the QCD critical point using the renormalization group, connecting it to the Ising universality class and analyzing the behavior of physical quantities.

Contribution

It provides a derivation of the universal equation of state for QCD near the critical point and explains how Ising universality applies to physical behavior with non-zero quark masses.

Findings

Universal equation of state near QCD critical point derived

Effective exponents depend on the approach path to the critical point

Critical region is smaller than previously expected

Abstract

We study the universal properties of the phase diagram of QCD near the critical point using the exact renormalization group. For two-flavour QCD and zero quark masses we derive the universal equation of state in the vicinity of the tricritical point. For non-zero quark masses we explain how the universal equation of state of the Ising universality class can be used in order to describe the physical behaviour near the line of critical points. The effective exponents that parametrize the growth of physical quantities, such as the correlation length, are given by combinations of the critical exponents of the Ising class that depend on the path along which the critical point is approached. In general the critical region, in which such quantities become large, is smaller than naively expected.