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

Abstract

Motivated by our earlier paper [Allahverdi R and Mazumdar A, Quasi-thermal universe andits implications for gravitino production, baryogenesis and dark matter, 2005 Preprinthep-ph/0505050], we discuss how the infamous gravitino problem has a natural built-insolution within supersymmetry. Supersymmetry allows a large number of flatdirections made up of gauge-invariant combinations of squarks and sleptons. Out ofmany, at least one generically obtains a large vacuum expectation value duringinflation. Gauge bosons and gauginos then obtain large masses by virtue of the Higgsmechanism. This makes the rate of thermalization after the end of inflation very smalland as a result the Universe enters a quasi-thermal phase after the inflaton hascompletely decayed. A full thermal equilibrium is generically established much later onwhen the flat direction expectation value has substantially decreased. This resultsin low reheat temperatures, i.e., , which are compatible with the stringent bounds arising from the big bangnucleosynthesis. There are two very important implications: the production ofgravitinos and generation of a baryonic asymmetry via leptogenesis during thequasi-thermal phase. In both the cases the abundances depend not only on an effectivetemperature of the quasi-thermal phase (which could be higher, i.e., ), 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 newparadigm based on a ‘quasi-thermal leptogenesis’, because in the bulk of theparameter space the old thermal leptogenesis cannot account for the observed baryonasymmetry.