Resonant decay of Bose condensates
  We present results of fully non-linear calculations of decay of the inflaton interacting with another scalar field X. Combining numerical results for cosmologically interesting range of resonance parameter, q \leq 10^6, with analytical estimates, we extrapolate them to larger q. We find that scattering of X fluctuations off the Bose condensate is a very efficient mechanism limiting growth of X fluctuations. For a single-component X, the resulting variance, at large q, is much smaller than that obtained in the Hartree approximation. 
S. Yu. Khlebnikov and I. I. Tkachev