Reconciling multi-messenger constraints with chiral symmetry restoration

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.