Dark-matter induced neutron-antineutron oscillations

TL;DR

This paper explores how light dark matter with baryon number could induce neutron-antineutron oscillations, especially via resonant effects, and analyzes axionic models to determine their viability in this context.

Contribution

It systematically analyzes axionic and scalar dark matter models for inducing neutron-antineutron oscillations, identifying constraints and potential experimental signatures.

Findings

Axion models do not induce oscillations due to experimental constraints.

Resonant n-nbar oscillations require a scalar or axion-like dark matter background.

Experimental signatures of dark matter-induced oscillations could be striking.

Abstract

If dark matter carries a baryon number of two, neutron-antineutron oscillations could require its presence to manifest themselves. If it is in addition very light, in the micro-eV range or up to a few orders of magnitude below, these oscillations could even exhibit a Rabi resonance. Though the magnetic tuning required to convert a macroscopic number of neutrons into antineutrons is not realistic, sizeable enhancements remain possible. Building on this observation, axionic realizations for this scenario are systematically analyzed. For true QCD axion models, we find that the Goldstone boson nature of the axion imposes the presence of axionless n-nbar mixing effects, either in vacuum or in decays, which are sufficiently constrained experimentally to leave no room for axion-induced oscillations. Thus, a generic scalar or axion-like dark matter background would have to exist to induce resonant n-nbar oscillations. Yet, if Nature has taken that path to relate dark matter and baryon number violation, the experimental signature would be striking and certainly worth pursuing.