Chiral symmetry restoration by parity doubling and the structure of neutron stars

Understand

We investigate the equation of state for a recently developed hybrid quark-meson-nucleon model under neutron star conditions of $\beta-$equilibrium and charge neutrality.

• The model has the characteristic feature that at increasing baryon density chiral symmetry is restored in a first order transition within the hadronic phase by lifting the mass splitting between chiral partner states, before quark deconfinement takes place.
• Most important for this study are the nucleon (neutron, proton) and $N(1535)$ states.
• We present three sets for the two free parameters which result in compact star mass-radius relations in accordance with modern constraints on the mass from PSR~J0437-4715 and on the compactness from GW170817.