Perturbative QCD and the Neutron Star Equation of State

TL;DR

This paper develops a model connecting nuclear theory and perturbative QCD to understand the neutron star equation of state, revealing how high-density physics influences astrophysical observations and the properties of neutron stars.

Contribution

It introduces a physics-agnostic approach linking low- and high-density constraints on the neutron star EoS, incorporating pQCD effects into astrophysical modeling.

Findings

pQCD influences the EoS mainly at densities higher than those in NS

pQCD prefers softer EoS for the heaviest neutron stars

Recent NICER data suggest a stiffer EoS, indicating a complex interplay

Abstract

We construct a physics-agnostic approach to the neutron star (NS) equation of state (EoS) based on a sound speed model, which connects both low-density information from nuclear theory and high-density constraints from perturbative QCD (pQCD). Using this approach, we study the impact of pQCD calculations on NS EoS that have been constrained by astrophysical observations. We find that pQCD affects the EoS mainly beyond the densities realized in NS. Furthermore, we observe an interesting interplay between pQCD and astrophysical constraints, with pQCD preferring softer EoS for the heaviest NS while recent NICER observations suggest the EoS to be stiffer. We explore the sensitivity of our findings to pQCD uncertainties and study the constraining power of pQCD if future observations of heavy NS were to suggest radii larger than 13 km.