Holographic quark matter with colour superconductivity and a stiff equation of state for compact stars

TL;DR

This paper develops a holographic QCD model predicting a stiff, deconfined quark phase with color superconductivity at high densities, leading to stable hybrid stars consistent with gravitational wave observations.

Contribution

It introduces a novel holographic approach to model quark matter with a first order phase transition and color superconductivity, predicting stable hybrid stars with observable signatures.

Findings

Predicts a stiff equation of state with a speed of sound close to light.

Finds stable hybrid stars with quark cores compatible with LIGO/Virgo data.

Shows a first order phase transition between different quark matter phases.

Abstract

We present a holographic model of QCD with a first order chiral restoration phase transition with chemical potential, mu. The first order behaviour follows from allowing a discontinuity in the dual description as the quarks are integrated out below their constituent mass. The model predicts a deconfined yet massive quark phase at intermediate densities (350 MeV< mu <500 MeV), above the nuclear density phase, which has a very stiff equation of state and a speed of sound close to one. We also include a holographic description of a colour superconducting condensate in the chirally restored vacuum and study the resulting equation of state. They provides a well behaved first order transition from the deconfined massive quark phase at very high density (mu>500 MeV). We solve the Tolman-Oppenheimer-Volkoff equations with the resulting equations of state and find stable hybrid stars with quark cores. We compute the tidal deformability for these hybrid stars and show they are consistent with LIGO/Virgo data on a neutron star collision. Our holographic model shows that quark matter could be present at the core of such compact stars.