Hybrid inflation and the moduli problem

We revisit some questions in supersymmetric hybrid inflation. We analyze the amount of fine-tuning required in various models, the problem of decay at the end of inflation and the generation of baryons after inflation. We find that the most natural setting for hybrid inflation is in supersymmetric models with nonrenormalizable couplings. Furthermore, we argue that almost inevitably, one of the fields involved is a modulus, with Planck scale variation. The resulting moduli problem can be solved in two ways: either by a massive modulus (which requires some fine-tuning), or an enhanced symmetry point, in which the moduli becomes strongly coupled to the standard model. Various possibilities for baryon production are discussed.