  Particle production from vacuum fluctuations during inflation is briefly
revisited. The moduli problem occurring with light particles produced at the
end of inflation is addressed, namely the fact that some results are in
disagreement with nucleosynthesis constrains. A universal solution to this
problem is found which leads to reasonable reheating temperatures in all cases.
It invokes the assumption that, immediately after inflation, the moduli evolve
like non-relativistic matter. The assumption is justified in the context of
massive chaotic inflation were, at the end of inflation, the universe evolves
as if it was matter-dominated.
