Re-reheating, late entropy injection and constraints from baryogenesis scenarios

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.