Gravitino Cosmology Helped by a Right Handed (S)Neutrino

TL;DR

This paper explores how the interplay between gravitinos and right-handed (s)neutrinos can address cosmological issues such as relic abundance and the $S_8$ tension through late-time decays and entropy production.

Contribution

It introduces scenarios where right-handed (s)neutrinos help resolve gravitino-related cosmological problems across different mass regimes.

Findings

Right-handed (s)neutrinos can produce late-time entropy to dilute gravitino relics.

Decaying gravitino dark matter can potentially resolve the $S_8$ tension.

Long-lived gravitinos with specific mass degeneracies are feasible within this framework.

Abstract

In this paper, we discuss interesting scenarios resulting from the interplay between the gravitino and the lightest right-handed (s)neutrino. We consider two gravitino mass regimes vastly separated, that is, $m_{3/2}=\mathcal{O}(100){\rm eV}$ and $m_{3/2}\simeq100{\rm GeV}$. For the former case, a significant amount of the entropy production in the cosmological history to dilute the gravitino relic abundance is unavoidable for consistency with the number of satellite galaxies in the Milky way. We will show that the right-handed (s)neutrino can play the role of the heavy particle whose late time decay provides such an additional radiation. For the later case, the gravitino of $m_{3/2}\simeq100{\rm GeV}$ may resolve the $S_{8}$ tension as a decaying dark matter. We will show how the lightest right-handed neutrino and its superpartner can help the gravitino decaying dark matter be equipped with a long enough life time and mass degeneracy with a massive decay product to address the $S_{8}$ tension.