Field evolution leading to hybrid inflation

In general the onset of hybrid inflation requires an extremely homogeneous field configuration at the end of the Planck era. The field φ orthogonal to the inflaton σ must be zero with the high accuracy over a region much larger than the initial horizon size ∼mPl−1. We consider a supersymmetric model that permits the decay of the oscillating field φ into light particles. We study the field evolution in this model and find that the requirement of extreme homogeneity can be relaxed. However, the mild condition of homogeneity should be still satisfied: the field φ must be smaller than the inflaton field σ by a factor of order 1 over a region exceeding the initial horizon size by about two orders of magnitude.