Unstable Neutrinos can Relax Cosmological Mass Bounds

Abstract

The light neutrino masses are at present most stringently constraint via cosmological probes. In particular the Planck collaboration reports $\sum m_{\nu }\le 0.12\mathrm{eV}$ at $95\%$ CL within the standard cosmological model. This is more than one order of magnitude stronger than the one arising from laboratory searches. The cosmological bound taken at face value excludes a plethora of neutrino flavour models which can successfully explain the neutrino oscillation data. The indirect nature of the cosmological bound, however, allows to relax the bound to up to $\sum m_{\nu }\sim 1\mathrm{eV}$ if neutrinos decay on timescales shorter than the age of the Universe, ${\tau }_{\nu }\le t_U$. We present how a decay of the type ${\nu }_i\to {\nu }_4\varphi$ can be realized within general models of the minimal extended seesaw framework. The idea is then explicitly realized within the context of a $U(1{)}_{\mu -\tau }$ flavour model.

Comments: Contribution to the 2022 EW session of the 56th Rencontres de Moriond