Resonant Decay of Cosmological Bose Condensates

We present results of fully nonlinear calculations of decay of the inflaton interacting with another scalar field $X$. Combining numerical results for a cosmologically interesting range of the resonance parameter, $q\le {10}^6$, 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.