Parity-Doubled Nucleons Can Rapidly Cool Neutron Stars.

Area of Science:

• Nuclear Physics
• Astrophysics
• Particle Physics

Background:

• Chiral symmetry breaking and restoration are key phenomena in confined hadronic matter.
• Nucleons (N_{+}) and their excited states of opposite parity (N_{-}) are fundamental to describing hadronic matter.

Purpose of the Study:

• To investigate the cooling mechanisms in cold, dense hadronic matter.
• To identify astrophysical signatures of chiral symmetry restoration.

Main Methods:

• Analysis of direct Urca decay processes involving N_{-} states.
• Comparison of cooling rates between N_{-} and N_{+} direct Urca processes at low temperature and moderate densities.

Main Results:

• Direct Urca decay processes involving N_{-} (e.g., N_{-}→N_{+}+e^{-}+ν[over ¯]_{e}) are possible when chiral symmetry is spontaneously broken.
• The cooling mediated by N_{-} decay dominates over standard N_{+} direct Urca processes due to the mass difference at low temperatures and moderate densities.

Conclusions:

• The dominance of N_{-} direct Urca cooling provides a strong astrophysical signature for chiral symmetry restoration in neutron stars.
• Understanding these processes is crucial for interpreting observations of neutron stars.