Phase structure and observables at high densities from first principles QCD

TL;DR

This paper reviews recent progress in applying functional QCD methods to understand the phase structure of QCD at high densities, including predictions of new phases and their potential experimental signatures.

Contribution

It provides a systematic overview of functional QCD approaches, their validation with lattice QCD, and new predictions for high-density phases beyond the chiral crossover.

Findings

Estimates for the onset of new phases at high density.

Predictions of experimental signatures for these phases.

Discussion of systematic uncertainties in the approach.

Abstract

We provide a short review of the progress made in the past decade with functional QCD in the description of the phase structure of QCD. We summarise the most important technical aspects of the framework, discuss strategies for truncations and address the problem of systematic error estimates. We detail efforts to gauge the approach systematically with lattice QCD at zero chemical potential, also including the physics of the Columbia plot at non-physical quark masses. Our main focus is, however, the high density regime of QCD. We address the predictive power of the functional approach for the appearance of new phases beyond the chiral crossover regime for chemical potentials $\mu_B/T\geq 4.5$. The onset of this regime may be signalled by a critical end point of the crossover line but may also involve a moat regime or the emergence of an instability that indicates an inhomogeneous phase. Respective results include estimates for the location of the onset of new phases, and predictions for their experimental signatures.