Energy-momentum tensor of cosmological fluctuations during inflation

Abstract
We study the renormalized energy-momentum tensor (EMT) of cosmological scalar fluctuations during the slow-rollover regime for chaotic inflation with a quadratic potential and find that it is characterized by a negative energy density which grows during slow rollover. We also approach the back-reaction problem as a second-order calculation in perturbation theory, finding no evidence that the back reaction of cosmological fluctuations is a gauge artifact. In agreement with the results for the EMT, the average expansion rate is decreased by the back reaction of cosmological fluctuations.