The energy-momentum tensor of quantum fluctuations in chaotic φ2 inflation

The study of the renormalized energy-momentum tensor (EMT) of quantum fluctuations in an inflationary universe driven by a massive scalar field is presented and compared with the known results in de Sitter space-time. When metric fluctuations are included, the renormalized EMT is characterized by a negative energy density which grows in time during the inflationary regime. We also approach the back-reaction problem as a second-order calculation in perturbation theory, and find that the average expansion rate is decreased, in agreement with the result on the EMT. Finally, we discuss common concerns and the implications of our results.