# Parity Doubling and the Dense Matter Phase Diagram under Constraints from Multi-Messenger Astronomy

## TL;DR

This paper extends a hybrid quark-meson-nucleon model to explore neutron-star properties, revealing how parity doubling and phase transitions influence the dense matter phase diagram and star characteristics.

## Contribution

It introduces a six-point scalar interaction into the model and analyzes its effects on neutron-star sequences and phase transitions under multi-messenger astronomy constraints.

## Key findings

- Model predicts parity doubling before quark deconfinement.
- Phase transition types depend on scalar field expectation.
- Mass-radius relations challenge observational constraints.

## Abstract

We extend the recently developed hybrid quark-meson-nucleon model by augmenting a six-point scalar interaction and investigate the consequences for neutron-star sequences in the mass-radius diagram. The model has the characteristic feature that, at increasing baryon density, the chiral symmetry is restored within the hadronic phase by lifting the mass splitting between chiral partner states (parity doubling), before quark deconfinement takes place. At low temperature and finite baryon density, the model predicts a first-, second-order chiral phase transition, or a crossover, depending on the expectation value of the scalar field, and a first-order deconfinement phase transition. We discuss two sets of free parameters, which result in compact-star mass-radius relations that are at tension with the combined constraints for maximum-mass ($2~M_\odot$) and the compactness (GW170817). We find that the most preferable mass-radius relations result in isospin-symmetric phase diagram with rather low temperature for the critical point of the chiral phase transition.