Dark Radiation or Warm Dark Matter from long lived particle decays in the light of Planck

TL;DR

This paper explores how long-lived particle decays can produce dark radiation or warm dark matter, potentially explaining observations from Planck and addressing the lithium problem.

Contribution

It introduces a scenario where particle decays produce dark radiation or warm dark matter, linking cosmological observations with particle physics.

Findings

Decays can produce fractional effective neutrino species compatible with Planck data.

Stable relics from decays can serve as warm dark matter candidates.

The model offers a potential solution to the lithium problem.

Abstract

Although Planck data supports the standard \Lambda CDM model, it still allows for the presence of Dark Radiation corresponding up to about half an extra standard neutrino species. We propose a scenario for obtaining a fractional "effective neutrino species" from a thermally produced particle which decays into a much lighter stable relic plus standard fermions. At lifetimes much longer than 1 sec, both the relic particles and the non-thermal neutrino component contribute to Dark Radiation. By increasing the stable-to-unstable particle mass ratio, the relic particle no longer acts as Dark Radiation but instead becomes a candidate for Warm Dark Matter with mass O(1keV - 100GeV). In both cases it is possible to address the lithium problem.