Reconciling multi-messenger constraints with chiral symmetry restoration

TL;DR

This paper demonstrates that a hadronic equation of state incorporating chiral symmetry restoration can reconcile various astrophysical constraints on neutron star properties, challenging the necessity of quark matter in stellar cores.

Contribution

It introduces a chiral symmetry-based hadronic EoS that aligns with multi-messenger neutron star observations, emphasizing the role of $elta$ matter and parity doubling.

Findings

The EoS can simultaneously satisfy mass, radius, and tidal deformability constraints.

Chiral symmetry restoration leads to $elta$ matter appearance, softening and stiffening the EoS.

Purely hadronic models may explain neutron star data without invoking quark matter.

Abstract

We analyze the recent astrophysical constraints in the context of a hadronic equation of state (EoS), in which the baryonic matter is subject to chiral symmetry restoration. We show that with such EoS it is possible to reconcile the modern constraints on the neutron star (NS) mass, radius, and tidal deformability (TD). We find that the softening of the EoS, required by the TD constraint of a canonical $1.4~M_\odot$ NS, followed by a subsequent stiffening, required by the $2~M_\odot$ constraint, is driven by the appearance of $\Delta$ matter due to partial restoration of chiral symmetry. Consequently, a purely hadronic EoS that accounts for the fundamental properties of quantum chromodynamics linked to the dynamical emergence of parity doubling with degenerate masses of nucleons and $\Delta$ resonances can be fully consistent with multi-messenger data. Therefore, with the present constraints on the EoS, the conclusion about the existence of the quark matter in the stellar core may still be premature.