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

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.

Comments: 4pages, 3figures, (ver2) Added discussions and corrected figure 2 and figure 3 following the mistake in the analysis (thanks to Simon Hands and Jon-Ivar Skullerud), (ver3) minor improvements, (ver4) minor improvements and references added