Crossover equation of state based on color-molecular-dynamics

TL;DR

This paper introduces a color molecular dynamics approach to model the equation of state for dense matter, successfully reproducing neutron star properties and suggesting quark matter may appear in their cores.

Contribution

The study develops a novel color molecular dynamics method to distinguish hadron and quark matter, aligning with observational constraints and exploring quark matter emergence in neutron star cores.

Findings

Mass-radius relations consistent with observations

Deconfined quark matter appears via crossover in neutron star cores

Model reproduces saturation properties of nuclear matter

Abstract

The equation of State for dense matter is studied with color molecular dynamics, in which hadron matter and quark matter are automatically distinguished only from quark color state. The quark-quark interactions are optimized to be consistent with saturation properties: symmetric energy, $L-$parameter, and incompressibility around nuclear density. In the calculations, the degrees of freedom of colors are solved at each numerical step, although the flavors are fixed as up or down quarks. The resultant mass-radius relations also satisfy the observational constraints such as the gravitational wave observations, NICER, and ``{\it the two-solar mass observations}" of neutron stars. In this model with the allowed parameter range, deconfined quark matter appears in the core of neutron stars via crossover. Although the current constraints from the observations are not enough to conclude whether quark matter appears at high-density region, our method would help to understand high-density material properties inside neutron stars in the future.