  We consider the single field chaotic m^2\phi^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
<\zeta\zeta> 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.
