Parity-doubled nucleons can rapidly cool neutron stars

TL;DR

This paper demonstrates that parity-doubled nucleons can significantly accelerate neutron star cooling via direct Urca processes involving excited states, revealing insights into chiral symmetry restoration in dense matter.

Contribution

It introduces the role of parity-doubled nucleons in neutron star cooling, highlighting a novel mechanism for rapid cooling linked to chiral symmetry restoration.

Findings

Parity-doubled nucleons enable faster neutron star cooling.

Direct Urca processes involving $N_{-}$ dominate at low temperatures.

Provides an astrophysical signature of chiral symmetry restoration.

Abstract

In confined hadronic matter, the spontaneous breaking and restoration of chiral symmetry can be described by considering nucleons, $N_{+}(939)$, and excited states of opposite parity, $N_{-}(1535)$. In a cold, dense hadronic phase where chiral symmetry remains spontaneously broken, direct Urca decay processes involving the $N_{-}$ are possible, e.g. $N_- \rightarrow N_+ + e^- + \bar{\nu}_e$. We show that at low temperature and moderate densities, because the $N_-$ is much heavier than the $N_+$, such cooling dominates over standard $N_+$ direct Urca processes. This provides a strong astrophysical signature of the pattern of chiral symmetry restoration in neutron stars.