Deconfinement in dense 2-color QCD

TL;DR

This paper investigates the phase structure of SU(2) lattice gauge theory with two flavors of Wilson fermions at finite chemical potential, identifying vacuum, Bose-Einstein condensed, and deconfined quark matter regimes with distinct observable signatures.

Contribution

It provides a detailed lattice study of deconfinement and superfluid phases in dense 2-color QCD, revealing non-perturbative screening effects and the nature of the quark matter phases.

Findings

Identification of three distinct mu-regimes: vacuum, Bose-Einstein condensation, and deconfined quark matter.

Observation of screening effects and a non-zero Polyakov loop in the high-density phase.

Evidence of a BCS diquark condensate disrupting the Fermi surface.

Abstract

We study SU(2) lattice gauge theory with two flavors of Wilson fermion at non-zero chemical potential mu and low temperature on a 8^3x16 system. We identify three regimes along the mu-axis. For mu<~m_pi/2 the system remains in the vacuum phase, and all physical observables considered remain essentially unchanged. The intermediate regime is characterised by a non-zero diquark condensate and an associated increase in the baryon density, consistent with what is expected for Bose-Einstein condensation of tightly bound diquarks. We also observe screening of the static quark potential here. In the high-density deconfined regime we find a non-zero Polyakov loop and a strong modification of the gluon propagator, including significant screening in the magnetic sector in the static limit, which must have a non-perturbative origin. The behaviour of thermodynamic observables and the superfluid order parameter are consistent with a Fermi surface disrupted by a BCS diquark condensate. The energy per baryon as a function of mu exhibits a minimum in the deconfined regime, implying that macroscopic objects such as stars formed in this theory are largely composed of quark matter.