Finite density nuclear matter and neutron stars in hard-wall AdS/QCD model

TL;DR

This paper models nuclear matter and neutron stars using a hard-wall AdS/QCD framework, revealing a chiral phase transition, pseudoconformal behavior at high densities, and producing neutron star properties aligned with observations.

Contribution

It introduces a novel homogeneous approximation in the hard-wall AdS/QCD model to study baryonic matter and neutron stars, capturing chiral symmetry restoration and pseudoconformal features.

Findings

Chiral phase transition occurs with decreasing chiral condensate at high density.

Speed of sound approaches the conformal limit in dense star cores.

Derived equation of state aligns with observational neutron star data.

Abstract

We investigate properties of nuclear matter, equation of state (EOS) of neutron stars and its mass-radius relation in a hard-wall AdS/QCD model by regarding baryons as solitonic configurations in gauge fields. Compared with previous approaches, we employ a different homogeneous approximation that takes into account the equations of motion for the pure gauge fields. By choosing appropriate parameters, we realize a chiral phase transition within the baryonic phase, where the chiral condensate decreases with the baryon chemical potential, until it reaches zero -- chiral symmetry is restored. In addition, independent of the existence of chiral phase transition, we also find that the speed of sound converges to the conformal limit at the density relevant to cores of massive stars but the trace of energy-momentum tensor does not vanish which indicates the pseudoconformal structure and intrinsic manifestation of scale symmetry in compact star matter. Through calculations, we obtain an equation of state that is more tightly constrained than previous works, and the resulting mass-radius relation of neutron stars is consistent with current observations.