Baryogenesis from Flat Directions of the Supersymmetric Standard Model

Baryogenesis from the coherent production of a scalar condensate along a flat direction of the supersymmetric extension of the standard model (Affleck-Dine mechanism) is investigated. Two important effects are emphasized. First, nonrenormalizable terms in the superpotential can lift standard model flat directions at large field values. Second, the finite energy density in the early universe induces soft potentials with curvature of order the Hubble constant. Both these have important implications for baryogenesis, which requires large squark or slepton expectation values to develop along flat directions. In particular, the induced mass squared must be negative. The resulting baryon to entropy ratio is very insensitive to the details of the couplings and initial conditions, but depends on the dimension of the nonrenormalizable operator in the superpotential which stabilizes the flat direction and the reheat temperature after inflation. Unlike the original scenario, an acceptable baryon asymmetry can result without subsequent entropy releases. In the simplest scenario the baryon asymmetry is generated along the $LH_u$ flat direction, and is related to the mass of the lightest neutrino.