Neutron-Mirror-Neutron Oscillation and Neutron Star Cooling

TL;DR

This paper revisits neutron-mirror-neutron oscillation constraints from neutron star cooling, revealing a new effect where mirror particle interactions can relax previous bounds, impacting terrestrial search prospects.

Contribution

It introduces a new effect involving mirror particle decay and interactions that significantly alters the existing neutron star cooling bounds on $n-n'$ oscillation rates.

Findings

Mirror particle decay creates a cloud inside neutron stars.

Mirror electron interactions can drain energy, relaxing cooling bounds.

The revised bounds impact terrestrial neutron oscillation searches.

Abstract

It was pointed out in a recent paper that the observed cooling rate of old, cold neutron stars (NS) can provide an upper limit on the transition rate of neutron to mirror neutron ($n-n'$). This limit is so stringent that it would preclude any discovery of $n \to n'$ oscillation in the current round of terrestrial searches for the process. Motivated by this crucially important conclusion, we critically analyze this suggestion and note an interesting new effect present in nearly exact mirror models for $n \to n'$ oscillation, which significantly affect this bound. The new element is the $\beta$ decay $n' \to p'+ e' +\bar{\nu}'_{e}$, which creates a cloud of mirror particles $n'$, $p'$, $e'$ and $D'$ inside the NS core. The $e'$ can "rob" the energy generated by the $n \to n'$ transition via $e-e'$ scattering enabled by the presence of a (minute) milli-charge in mirror particles. This energy is emitted as unobserved mirror photons via fast mirror bremsstrahlung leading to a relaxation of this upper limit.