Constraints for the QCD phase diagram from imaginary chemical potential

TL;DR

This paper provides lattice simulation evidence for tricritical points in the QCD phase diagram at imaginary chemical potential, revealing the structure of critical surfaces and their implications for phase transition behavior at real chemical potential.

Contribution

It identifies and characterizes tricritical points in the QCD phase diagram at imaginary chemical potential, elucidating the structure of critical surfaces and their impact on phase transitions.

Findings

Existence of two tricritical points in the (T,m) phase diagram at fixed imaginary chemical potential.

The shape of the deconfinement critical surface is governed by tricritical scaling.

Deconfinement transition weakens with increasing real chemical potential.

Abstract

We present unambiguous evidence from lattice simulations of N_f=3 QCD for two tricritical points in the (T,m) phase diagram at fixed imaginary \mu/T=i\pi/3 mod. 2\pi/3, one in the light and one in the heavy quark regime. Together with similar results in the literature for N_f=2 this implies the existence of a chiral and of a deconfinement tricritical line at those values of imaginary chemical potentials. These tricritical lines represent the boundaries of the analytically continued chiral and deconfinement critical surfaces, respectively, which delimit the parameter space with first order phase transitions. It is demonstrated that the shape of the deconfinement critical surface is dictated by tricritical scaling and implies the weakening of the deconfinement transition with real chemical potential. A qualitatively similar effect holds for the chiral critical surface.