Leptogenesis, Gravitino Dark Matter and Entropy Production
  Many extensions of the Standard Model predict super-weakly interacting
particles, which typically have to decay before Big Bang Nucleosynthesis (BBN).
The entropy produced in the decays may help to reconcile thermal leptogenesis
and BBN in scenarios with gravitino dark matter, which is usually difficult due
to late decays of the next-to-lightest supersymmetric particle (NLSP) spoiling
the predictions of BBN. We study this possibility for a general neutralino
NLSP. We elaborate general properties of the scenario and strong constraints on
the entropy-producing particle. As an example, we consider the saxion from the
axion multiplet and show that, while enabling a solution of the strong CP
problem, it can also produce a suitable amount of entropy.
