Light Scalars and the Generation of Density Perturbations During   Preheating or Inflaton Decay
  Reheating after inflation can occur through inflaton decay or efficient parametric resonant production of particles from the oscillation of the inflaton. If the particles produced interact with scalars that were light during inflation, then significant super-horizon density perturbations are generated during this era. These perturbations can be highly non-Gaussian. 
Lotty Ackerman, Christian W. Bauer, Michael L. Graesser, Mark B. Wise