Introducing the concept of the Widom line in the QCD phase diagram

TL;DR

This paper extends the concept of the Widom line, a supercritical crossover phenomenon, into the QCD phase diagram, suggesting it can explain thermodynamic anomalies near the critical end point of the hadron gas to quark-gluon plasma transition.

Contribution

It introduces the Widom line into QCD, linking critical phenomena in fluids to the phase structure of strongly interacting matter.

Findings

Thermodynamic anomalies in QCD models can be interpreted as manifestations of the Widom line.

The existence of a Widom line in QCD implies new insights into the supercritical region of the phase diagram.

Possible new directions for research on the QCD phase diagram using the Widom line concept.

Abstract

Critical phenomena emerging from the critical end point of a first-order transition are ubiquitous in nature. Here we bring the concept of a supercritical crossover, the Widom line, initially developed in the context of fluids, into the interacting matter described by quantum chromodynamics (QCD). We show that the existence of the putative critical end point between hadron gas and quark-gluon plasma in the temperature versus chemical potential of the QCD phase diagram implies the existence of a Widom line emerging from it in the supercritical region. We survey the thermodynamic anomalies already identified in simplified theoretical models of QCD exhibiting a critical end point, to show that they can be interpreted in terms of a Widom line. Then we suggest possible directions where the Widom line concept could provide new light on the QCD phase diagram.