Velocity of Sound beyond the High-Density Relativistic Limit from Lattice Simulation of Dense Two-Color QCD

TL;DR

This study uses lattice simulations to explore the equation of state for dense two-color QCD, revealing that the sound velocity surpasses the relativistic limit after the BEC-BCS crossover, a novel finding with potential astrophysical implications.

Contribution

It demonstrates for the first time from lattice QCD calculations that the sound velocity exceeds the relativistic limit in dense matter, beyond previous theoretical expectations.

Findings

Sound velocity exceeds the relativistic limit after BEC-BCS crossover.

First lattice QCD evidence of superluminal sound speed in dense matter.

Potential implications for neutron star equation of state.

Abstract

We obtain the equation of state (EoS) for two-color QCD at low temperature and high density from the lattice Monte Carlo simulation. We find that the velocity of sound exceeds the relativistic limit ($c_s^2/c^2=1/3$) after BEC-BCS crossover in the superfluid phase. Such an excess of the sound velocity is previously unknown from any lattice calculations for QCD-like theories. This finding might have a possible relevance to the EoS of neutron star matter revealed by recent measurements of neutron star masses and radii.