  I review my recent work with Brian Greene and Thomas Roos. First I discuss
the effect of a negative cross-coupling on the inflaton decay in two scalar
field theories. Our main finding is a new effect, the negative coupling
instability, which leads to explosive particle production and very fast
inflaton decay. Then I discuss the consequences of this instability for
grandunified baryogenesis models. The novel aspect of this review is an
intuitive explanation of the negative coupling instability, using field
trajectories in the configuration space.
