Dark Matter Decaying into a Fermi Sea of Neutrinos

TL;DR

This paper explores the decay of a scalar dark matter field into neutrinos, analyzing how Pauli blocking and universe expansion affect decay rates and implications for cosmic structure formation.

Contribution

It introduces a novel scenario of dark matter decay into neutrinos with a time-varying decay rate influenced by universe expansion and Pauli blocking effects.

Findings

Decay rate varies across cosmological epochs.

Decay into neutrinos impacts structure formation.

Potential to alleviate cold dark matter problems.

Abstract

We study the possible decay of a coherently oscillating scalar field, interpreted as dark matter, into light fermions. Specifically, we consider a scalar field with sub-eV mass decaying into a Fermi sea of neutrinos. We recognize the similarity between our scenario and inflationary preheating where a coherently oscillating scalar field decays into standard model particles. Like the case of fermionic preheating, we find that Pauli blocking controls the dark matter decay into the neutrino sea. The radius of the Fermi sphere depends on the expansion of the universe leading to a time varying equation of state of dark matter. This makes the scenario very rich and we show that the decay rate might be different at different cosmological epochs. We categorize this in two interesting regimes and then study the cosmological perturbations to find the impact on structure formation. We find that the decay may help alleviating some of the standard problems related to cold dark matter.