Towards the phase diagram of dense two-color matter

TL;DR

This study explores the phase diagram of dense two-color QCD, revealing a superfluid phase with nearly-free quarks disrupted by BCS pairing, and a transition to deconfined quark matter at higher temperature and chemical potential.

Contribution

It provides new insights into the phase structure of two-color QCD, especially the nature of superfluid and deconfined phases, using lattice simulations with Wilson fermions.

Findings

Identification of a superfluid phase with BCS pairing.

Evidence of a deconfined quark matter phase at high T and mu.

Quark number susceptibility remains unchanged at deconfinement.

Abstract

We study two-color QCD with two flavors of Wilson fermion as a function of quark chemical potential mu and temperature T. We find evidence of a superfluid phase at intermediate mu and low T where the quark number density and diquark condensate are both very well described by a Fermi sphere of nearly-free quarks disrupted by a BCS condensate. Our results suggest that the quark contribution to the energy density is negative (and balanced by a positive gauge contribution), although this result is highly sensitive to details of the energy renormalisation. We also find evidence that the chiral condensate in this region vanishes in the massless limit. This region gives way to a region of deconfined quark matter at higher T and mu, with the deconfinement temperature, determined from the renormalised Polyakov loop, decreasing only very slowly with increasing chemical potential. The quark number susceptibility chi_q does not exhibit any qualitative change at the deconfinement transition. We argue that this is because chi_q is not an appropriate measure of deconfinement for 2-color QCD at high density.