  Many theories of particle physics beyond the Standard Model predict
long-lived fields that may have dominated the Universe at early times and then
decayed. Their decay, which injects entropy in the thermal bath, is responsible
for a second reheating, dubbed re-reheating, that could substantially dilute
the matter-antimatter asymmetry created before. In this paper we analyze such
late re-reheating and entropy dilution. It turns out that in some cases the
usual analytic calculation badly fails if it is not rectified by some
corrective factors that we provide. We also determine the parameter space where
the entropy dilution compromises models of baryogenesis. This region can be
obtained by imposing some generic constraints that are applicable to any
baryogenesis mechanism and long-lived field satisfying a few assumptions. For
instance, by applying them to MSSM electroweak baryogenesis, thermal
non-resonant leptogenesis and thermal resonant leptogenesis, we obtain that the
initial abundances of long-lived fields with lifetime longer than respectively
5*10^13, 10^-2 and 10^15 GeV^-1 are strongly constrained. Similarly, the same
baryogenesis scenarios are incompatible with large oscillations of moduli with
mass smaller than O(10^8), O(10^13) and O(10^7) GeV that are naturally coupled
to the visible sector via gravitational dimension-five operators.
