# New Neutron Star Equation of State with Quark-Hadron Crossover

## TL;DR

This paper introduces an improved neutron star equation of state, QHC19, featuring a smooth hadron-quark crossover, aligning well with observational data and providing new insights into dense matter physics.

## Contribution

The paper develops a novel neutron star equation of state with a continuous hadron-quark transition, integrating advanced models for both regimes and constraining key interaction parameters.

## Key findings

- QHC19 matches GW170817 data on neutron star properties.
- Maximum neutron star mass predicted is 2.35 solar masses.
- The model provides a consistent description of matter at all densities.

## Abstract

We present a much improved equation of state for neutron star matter, QHC19, with a smooth crossover from the hadronic regime at lower densities to the quark regime at higher densities. We now use the Togashi et al.~equation of state (Togashi:2017), a generalization of the Akmal-Pandharipande-Ravenhall equation of state of uniform nuclear matter, in the entire hadronic regime; the Togashi equation of state consistently describes non-uniform as well as uniform matter, and matter at beta equilibrium without the need for an interpolation between pure neutron and symmetric nuclear matter. We describe the quark matter regime at higher densities with the Nambu--Jona--Lasinio model, now identifying tight constraints on the phenomenological universal vector repulsion between quarks and the pairing interaction between quarks arising from the requirements of thermodynamic stability and causal propagation of sound. The resultant neutron star properties agree very well with the inferences of the LIGO/Virgo collaboration, from GW170817, of the pressure vs. baryon density, neutron star radii, and tidal deformabilities. The maximum neutron star mass allowed by QHC19 is 2.35 $M_\odot$, consistent with all neutron star mass determinations.