Cosmological consequences of supersymmetric flat directions

In this work we analyze various implications of the presence of large field vacum expectation values (VEVs) along supersymmetric flat direct ions during the early universe. First, we discuss supersymmetric leptogenesis and the grav itino bound. Supersym- metric thermal leptogenesis with a hierarchical right-han ded neutrino mass spectrum normally requires the mass of the lightest right-handed neu trino to be heavier than about 10 9 GeV. This is in conflict with the upper bound on the reheating t empera- ture which is found by imposing that the gravitinos generate d during the reheating stage after inflation do not jeopardize successful nucleosy nthesis. We show that a solution to this tension is actually already incorporated i n the framework, because of the presence of flat directions in the supersymmetric scalar potential. Massive right- handed neutrinos are efficiently produced non-thermally and the observed baryon asymmetry can be explained even for a reheating temperature respecting the grav- itino bound if two conditions are satisfied: the initial valu e of the flat direction must be close to Planckian values and the phase-dependent terms i n the flat direction potential are either vanishing or sufficiently small. We then show that flat directions also contribute to the total curvature perturbation. Such perturbation is generated at the first oscillation of th e flat direction condensate when the latter relaxes to the minimum of its potential after the end of inflation. If the contribution to the total curvature perturbation fro m supersymmetric flat direction is the dominant one, then a significant level of non -Gaussianity in the cosmological perturbation is also naturally expected. Finally, we argue that supersymmetric flat direction VEVs ca n decay non pertur- batively via preheating even in the case where they undergo e lliptic motion in the complex plane instead of radial motion through the origin. I t has been generally argued that in this case adiabaticity is never violated and p reheating is inefficient. Considering a toy U (1) gauge theory, we explicitly calculate the scalar potent ial, in the unitary gauge, for excitations around several flat dir ections. We show that the mass matrix for the excitations has non-diagonal entrie s which vary with the phase of the flat direction vacuum expectation value. Furthe rmore, this mass matrix has zero eigenvalues whose eigenstates change with time. We show that these light degrees of freedom are produced copiously in the non-pertur bative decay of the flat direction VEV.