Dark decay of the neutron

TL;DR

This paper investigates a novel neutron decay channel into dark matter particles and a dark photon, analyzing constraints from neutron stars, dark matter detection, supernovae, and cosmology to identify viable parameter space.

Contribution

It introduces a decay mode involving a dark Dirac fermion and dark photon, and delineates conditions under which this scenario remains consistent with existing astrophysical and experimental constraints.

Findings

Decay into dark matter and dark photon can be viable if certain mass and coupling ratios are met.

Neutron star constraints are satisfied for specific dark photon mass to coupling ratios.

Dark photon and kinetic mixing parameters are tightly constrained by detection and cosmological data.

Abstract

New decay channels for the neutron into dark matter plus other particles have been suggested for explaining a long-standing discrepancy between the neutron lifetime measured from trapped neutrons versus those decaying in flight. Many such scenarios are already ruled out by their effects on neutron stars, and the decay into dark matter plus photon has been experimentally excluded. Here we explore the decay into a dark Dirac fermion $\chi$ and a dark photon $A'$, which can be consistent with all constraints if $\chi$ is a subdominant component of the dark matter. Neutron star constraints are evaded if the dark photon mass to coupling ratio is $m_{A'}/g' \lesssim (45-60)\,$MeV, depending upon the nuclear equation of state. $g'$ and the kinetic mixing between U(1)$'$ and electromagnetism are tightly constrained by direct and indirect dark matter detection, supernova constraints, and cosmological limits.