Supersymmetric thermalization and quasi-thermal Universe: consequences for gravitinos and leptogenesis

Motivated by our earlier paper [Allahverdi R and Mazumdar A, Quasi-thermal universe and its implications for gravitino production, baryogenesis and dark matter, 2005 Preprint hep-ph/ 0505050], we discuss how the infamous gravitino problem has a natural built-in solution within supersymmetry. Supersymmetry allows a large number of. at directions made up of gauge-invariant combinations of squarks and sleptons. Out of many, at least one generically obtains a large vacuum expectation value during inflation. Gauge bosons and gauginos then obtain large masses by virtue of the Higgs mechanism. This makes the rate of thermalization after the end of inflation very small and as a result the Universe enters a quasi-thermal phase after the inflaton has completely decayed. A full thermal equilibrium is generically established much later on when the. at direction expectation value has substantially decreased. This results in low reheat temperatures, i.e., TR similar to O ( TeV), which are compatible with the stringent bounds arising from the big bang nucleosynthesis. There are two very important implications: the production of gravitinos and generation of a baryonic asymmetry via leptogenesis during the quasi-thermal phase. In both the cases the abundances depend not only on an effective temperature of the quasi-thermal phase ( which could be higher, i.e., T >> TR), but also on the state of equilibrium in the reheat plasma. We show that there is no 'thermal gravitino problem' at all within supersymmetry and we stress the need for a new paradigm based on a 'quasi-thermal leptogenesis', because in the bulk of the parameter space the old thermal leptogenesis cannot account for the observed baryon asymmetry.