Constraining models for keV sterile neutrinos by quasi-degenerate active neutrinos

TL;DR

This paper proves a No-Go theorem showing that keV sterile neutrino dark matter models with quasi-degenerate active neutrinos are incompatible with astrophysical X-ray constraints within certain theoretical frameworks.

Contribution

It provides a general proof of a No-Go theorem that constrains keV sterile neutrino models, especially those with real Casas-Ibarra matrices and no CP violation.

Findings

Astrophysical X-ray bounds conflict with quasi-degenerate active neutrinos in certain models

The theorem applies broadly to models without CP violation and real R matrices

Future experiments could exclude entire classes of keV sterile neutrino models

Abstract

We present a No-Go theorem for keV sterile neutrino Dark Matter: if sterile neutrinos at the keV scale play the role of Dark Matter, they are typically unstable and their decay produces an astrophysical monoenergetic X-ray line. It turns out that the observational bound on this line is so strong that it contradicts the existence of a quasi-degenerate spectrum of active neutrinos in a seesaw type I framework where the Casas-Ibarra matrix R is real. This is the case in particular for models without CP violation. We give a general proof of this theorem. While the theorem (like every No-Go theorem) relies on certain assumptions, the situation under which it applies is still sufficiently general to lead to interesting consequences for keV neutrino model building. In fact, depending on the outcome of the next generation experiments, one might be able to rule out whole classes of models for keV sterile neutrinos.