Two-color quark matter: U(1)_A restoration, superfluidity, and quarkyonic phase

TL;DR

This paper explores the phase structure of two-color QCD with two light quark flavors, focusing on U(1)_A symmetry restoration, superfluidity, and the quarkyonic phase, providing predictions testable by lattice simulations.

Contribution

It demonstrates that two-color QCD can model key features of the QCD phase diagram, including the quarkyonic phase and U(1)_A restoration, without the sign problem.

Findings

Identification of conditions for U(1)_A symmetry restoration.

Prediction of coexistence of quarkyonic matter and diquark condensation.

Quantitative results from the extended NJL model applicable to lattice tests.

Abstract

We discuss the phase structure of quantum chromodynamics (QCD) with two colors and two flavors of light quarks. This is motivated by the increasing interest in the QCD phase diagram as follows: (1) The QCD critical point search has been under intensive dispute and its location and existence suffer from uncertainty of effective U(1)_A symmetry restoration. (2) A new phase called quarkyonic matter is drawing theoretical and experimental attention but it is not clear whether it can coexist with diquark condensation. We point out that two-color QCD is nontrivial enough to contain essential ingredients for (1) and (2) both, and most importantly, is a system without the sign problem in numerical simulations on the lattice. We adopt the two-flavor Nambu-Jona-Lasinio model extended with the two-color Polyakov loop and make quantitative predictions which can be tested by lattice simulations.