Cosmological constraints on the decay of heavy relics into neutrinos

TL;DR

This paper investigates how decaying heavy relic particles into neutrinos in the early Universe can be constrained through cosmological observations, considering secondary electromagnetic emissions and their effects on CMB and nucleosynthesis.

Contribution

It provides new, stringent bounds on the lifetime of heavy relic particles decaying into neutrinos based on cosmological probes, accounting for secondary electromagnetic emissions.

Findings

Strong bounds on relic particle lifetime for short-lived particles.

Secondary electromagnetic emissions significantly constrain neutrino decay scenarios.

Cosmological probes like CMB and BBN are sensitive to these decays.

Abstract

A massive particle decaying into neutrinos in the early Universe is known to be less constrained than if it was decaying into other standard model particles. However, even if the decay proceeds into neutrinos, the latter still inevitably emit secondary particles undergoing electromagnetic interactions that can be probed. We analyse in details how sensitive various cosmological probes are to such secondary particles, namely CMB anisotropies, CMB spectral distortions, and Big Bang Nucleosynthesis. For relics whose lifetime is shorter than the age of the Universe, this leads to original and stringent bounds on the particle's lifetime as a function of its abundance and mass.