Gravitino Cosmology Helped by a Right Handed (S)Neutrino
  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.
