The pseudo-Goldstone spectrum of 2-colour QCD at finite density

TL;DR

This study investigates the spectrum of 2-colour lattice QCD at finite chemical potential, revealing a phase transition with diquark condensation and analyzing the behavior of pseudo-Goldstone bosons, highlighting both qualitative agreement and discrepancies with effective theories.

Contribution

It provides the first lattice evidence of a mean-field phase transition to a diquark condensate in 2-colour QCD at finite density and compares the spectrum to chiral effective Lagrangian predictions.

Findings

Transition to diquark condensate at μ=m_π/2

Qualitative agreement with effective Lagrangians for μ < m_π/2

Discrepancies at higher μ likely due to lattice saturation artifacts

Abstract

We examine the spectrum of 2-colour lattice QCD with 4 continuum flavours at a finite chemical potential ($\mu$) for quark-number, on a $12^3 \times 24$ lattice. First we present evidence that the system undergoes a transition to a state with a diquark condensate, which spontaneously breaks quark number at $\mu=m_\pi/2$, and that this transition is mean field in nature. We then examine the 3 states that would be Goldstone bosons at $\mu=0$ for zero Dirac and Majorana quark masses. The predictions of chiral effective Lagrangians give a good description of the behaviour of these masses for $\mu < m_\pi/2$. Except for the heaviest of these states, these predictions diverge from our measurements, once $\mu$ is significantly greater than $m_\pi/2$. However, the qualitative behaviour of these masses, indicates that the physics is very similar to that predicted by these effective Lagrangians, and there is some indication that at least part of these discrepancies is due to saturation, a lattice artifact.