Holographic equations of state and astrophysical compact objects

TL;DR

This paper investigates holographic equations of state for neutron stars, finding that D4/D6 models can support stable compact stars, unlike D4/D8 models which cannot.

Contribution

It demonstrates that certain holographic QCD models, specifically D4/D6, can produce stable neutron star solutions, advancing the application of holography in astrophysics.

Findings

D4/D8 model does not support stable stars.

D4/D6 models support stable compact stars.

Holographic stars have larger mass and radius than typical neutron stars.

Abstract

We solve the Tolman-Oppenheimer-Volkoff equation using an equation of state (EoS) calculated in holographic QCD. The aim is to use compact astrophysical objects like neutron stars as an indicator to test holographic equations of state. We first try an EoS from a dense D4/D8/\textoverline {D8} model. In this case, however, we could not find a stable compact star, a star satisfying pressure-zero condition with a radius $R$, $p(R)=0$, within a reasonable value of the radius. This means that the EoS from the D4/D8/\textoverline {D8} model may not support any stable compact stars or may support one whose radius is very large. This might be due to a deficit of attractive force from a scalar field or two-pion exchange in the D4/D8/\textoverline {D8} model. Then, we consider D4/D6 type models with different number of quark flavors, $N_f=1,2,3$. Though the mass and radius of a holographic star is larger than those of normal neutron stars, the D4/D6 type EoS renders a stable compact star.