Mapping the QCD Phase Diagram

TL;DR

This paper reviews theoretical advances in mapping the QCD phase diagram, focusing on the critical point discovery and understanding cold dense quark matter, including color superconductivity in neutron stars.

Contribution

It synthesizes recent theoretical insights on the QCD phase diagram, highlighting the potential discovery of the critical point and exploring color superconductivity in dense quark matter.

Findings

Identification of the critical point as a key feature of the QCD phase diagram

Progress in understanding color superconductivity in neutron star cores

Implications for experimental mapping of the phase diagram

Abstract

I review recent theoretical developments which show how a key qualitative feature of the QCD phase diagram, namely a critical point which in a sense defines the landscape which heavy ion collision experiments are seeking to map, can be discovered. The map of the phase diagram which I sketch is based on reasonable inference from universality, lattice gauge theory and models; the discovery of the critical point would provide an experimental foundation for the central qualitative feature of the landscape. I also review recent progress in our understanding of cold, dense quark matter, as may occur in the cores of neutron stars. In this regime, quarks form Cooper pairs. The formation of such superconducting phases requires only weak attractive interactions, as provided by one-gluon exchange at asymptotically high density; these phases may nevertheless break chiral symmetry (by locking flavor symmetries to color symmetry) and may have excitations which are indistinguishable from those in a confined phase. Mapping this part of the phase diagram will require a better understanding of how the presence of color superconductivity and color-flavor locking affects neutron star phenomenology.