Neutron stars and phase diagram in a hard-wall AdS/QCD model

TL;DR

This paper explores the phase diagram of large-Nc QCD using a holographic hard-wall model, revealing various phases, a baryonic popcorn transition, and implications for neutron star properties and gravitational wave signals.

Contribution

It introduces a simplified holographic model with a dynamical scalar and homogeneous Ansatz to study QCD phases and neutron star phenomena.

Findings

Qualitative phase diagram consistent with expectations.

Identification of a baryonic popcorn transition at high chemical potential.

Neutron star models with stiff equations of state and gravitational wave predictions.

Abstract

We study the phase diagram of (large-$N_c$) QCD using a simplistic holographic hard-wall model with a dynamical scalar field and a homogeneous Ansatz representing a smeared instanton/baryon density. The resulting phase diagram is qualitatively consistent with expectations, including a mesonic, baryonic, quarkyonic, and quark-gluon plasma phase. As in other holographic models, we also find a baryonic popcorn transition, which appears at large chemical potential as a crossover. We then evaluate the nuclear matter equation of state, which turns out to be rather stiff with a large peaked sound velocity above the conformal limit, construct corresponding neutron stars using the TOV equations, and finally use a full numerical gravity/hydrodynamics computation to extract the gravitational wave signal of neutron star mergers.