The axial anomaly and the phases of dense QCD

TL;DR

This paper discusses how the QCD axial anomaly influences the phase diagram of dense quark matter, revealing a new critical point that suggests a smooth crossover between hadronic and quark phases at low temperatures, with implications for neutron stars.

Contribution

It introduces a new critical point in the QCD phase diagram caused by the axial anomaly, connecting phase transitions with BEC-BCS crossover phenomena and astrophysical implications.

Findings

Existence of a new critical point in the QCD phase diagram.

Smooth crossover from hadronic to quark matter at low temperature.

Potential implications for quark matter in neutron stars.

Abstract

The QCD axial anomaly, by coupling the chiral condensate and BCS pairing fields of quarks in dense matter, leads to a new critical point in the QCD phase diagram \cite{HTYB,chiral2}, which at sufficiently low temperature should terminate the line of phase transitions between chirally broken hadronic matter and color superconducting quark matter. The critical point indicates that matter at low temperature should cross over smoothly from the hadronic to the quark phase, as suggested earlier on the basis of symmetry. We review here the arguments, based on a general Ginzburg-Landau effective Lagrangian, for the existence of the new critical point, as well as discuss possible connections between the QCD phase structure and the BEC-BCS crossover in ultracold trapped atomic fermion systems at unitarity. and implications for the presence of quark matter in neutron stars.