  At the end of inflation the Universe is frozen in a near zero-entropy state
with energy density in a coherent scalar field and must be "defrosted" to
produce the observed entropy and baryon number. Baryon asymmetry may be
generated by the decay of supermassive Grand Unified Theory (GUT) bosons
produced non-thermally in a preheating phase after inflation, thus solving many
drawbacks facing GUT baryogenesis in the old reheating scenario.
