We consider the single field chaotic m^2phi^2 inflationary model with a period of preheating, where the inflaton decays to another scalar field chi in the parametric resonance regime. In a recent work, one of us has shown that the chi modes circulating in the loops during preheating notably modify the <zetazeta> correlation function. We first rederive this result using a different gauge condition hence reconfirm that superhorizon zeta modes are affected by the loops in preheating. Further, we examine how chi loops give rise to non-gaussianity and affect the tensor perturbations. For that, all cubic and some higher order interactions involving two chi fields are determined and their contribution to the non-gaussianity parameter f_{NL} and the tensor power spectrum are calculated at one loop. Our estimates for these corrections show that while a large amount of non-gaussianity can be produced during reheating, the tensor power spectrum receive moderate corrections. We observe that the loop quantum effects increase with more chi fields circulating in the loops indicating that the perturbation theory might be broken down. These findings demonstrate that the loop corrections during reheating are significant and they must be taken into account for precision inflationary cosmology.
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