Bump of sound velocity in dense 2-color QCD

TL;DR

This paper investigates the equation of state and sound velocity in dense 2-color QCD, revealing superfluid phase properties and a peak in sound velocity at high density, with implications for theoretical bounds.

Contribution

It provides the first detailed calculation of sound velocity in dense 2-color QCD across different phases, including superfluid and BCS regimes, consistent with chiral perturbation theory.

Findings

Superfluid phase has sound velocity squared greater than 1/3 of the speed of light.

Sound velocity peaks in the high-density BCS phase.

Results align with chiral perturbation theory predictions.

Abstract

We obtain the equation of state (EoS) and the sound velocity for 2-color QCD at low temperature and high density and find that in the superfluid phase, $c_s^2/c^2 >1/3$, where $1/3$ is the value at the relativistic limit. Several independent Monte Carlo studies on 2-color QCD have been conducted intensively in recent years. These works have shown a clear evidence of phase transition between hadronic and superfluid phases. In our paper[1], we have investigated the EoS and sound velocity in both phases. Our result is consistent with chiral perturbation theory in a low $\mu$ regime of the superfluid phase including the Bose-Einstein condensed phase, and shows a peak of sound velocity in the high-density BCS phase. We also give detailed simulation results and a comment on the holography bound in this proceedings.