Monochromatic neutrinos generated by dark matter and the see-saw mechanism

TL;DR

This paper proposes a minimal extension of the Standard Model where a scalar field coupled to right-handed neutrinos can serve as a dark matter candidate, producing monochromatic neutrino signals detectable by neutrino observatories.

Contribution

It introduces a novel dark matter candidate scalar linked to the see-saw mechanism, with specific decay modes and potential observational signatures in neutrino detectors.

Findings

Scalar A has a long lifetime, exceeding the age of the universe.

Below 8 TeV, A decays predominantly into neutrino pairs.

Detectable monochromatic neutrino signals are possible with current observatories.

Abstract

We study a minimal extension of the Standard Model where a scalar field is coupled to the right handed neutrino responsible for the see-saw mechanism for neutrino masses. In the absence of other couplings, below 8 TeV the scalar $A$ has a unique decay mode $A \rightarrow \nu \nu$, $\nu$ being the physical observed light neutrino state. Above 8 (11) TeV, the 3-body (4-body) decay modes dominate. Imposing constraints on neutrino masses $m_\nu$ from atmospheric and solar experiments implies a long lifetime for $A$, much larger than the age of the Universe, making it a natural dark matter candidate. Its lifetime can be as large as $10^{29}$ seconds, and its signature below 8 TeV would be a clear monochromatic neutrino signal, which can be observed by ANTARES or IceCube. Under certain conditions, the scalar $A$ may be viewed as a Goldstone mode of a complex scalar field whose vacuum expectation value generates the Majorana mass for $\nu_R$. In this case, we expect the dark matter scalar to have a mass $\lesssim 10$ GeV.