Confining but chirally symmetric dense and cold matter

TL;DR

This paper reviews the theoretical possibility of a phase of cold, dense matter that remains confining yet exhibits restored chiral symmetry, based on hadron spectroscopy and QCD mechanisms.

Contribution

It proposes a mechanism for confining but chirally symmetric matter at high density, linking spectroscopy evidence to phase transition possibilities.

Findings

Parity doubling in excited hadrons suggests chiral symmetry restoration.

Chirally symmetric quark Green functions remain infrared divergent under confinement.

A first-order phase transition to confining but chirally symmetric matter is likely.

Abstract

The possibility for existence of cold, dense chirally symmetric matter with confinement is reviewed. The answer to this question crucially depends on the mechanism of mass generation in QCD and interconnection of confinement and chiral symmetry breaking. This question can be clarified from spectroscopy of hadrons and their axial properties. Almost systematical parity doubling of highly excited hadrons suggests that their mass is not related to chiral symmetry breaking in the vacuum and is approximately chirally symmetric. Then there is a possibility for existence of confining but chirally symmetric matter. We clarify a possible mechanism underlying such a phase at low temperatures and large density. Namely, at large density the Pauli blocking prevents the gap equation to generate a solution with broken chiral symmetry. However, the chirally symmetric part of the quark Green function as well as all color non-singlet quantities are still infrared divergent, meaning that the system is with confinement. A possible phase transition to such a matter is most probably of the first order. This is because there are no chiral partners to the lowest lying hadrons.