Adiabatic regularization of the graviton stress-energy tensor in de Sitter space-time

TL;DR

This paper investigates the renormalized energy-momentum tensor of gravitons in de Sitter space-time, revealing that graviton fluctuations increase the scalar expansion rate and could influence inflationary models.

Contribution

It applies adiabatic regularization to gravitons in de Sitter space, showing their positive energy density contribution and potential role in inflation dynamics.

Findings

Graviton energy density is proportional to H^4 with a positive sign.

Graviton fluctuations increase the gauge-invariant expansion rate.

Implications for gravitons driving inflation in the Starobinsky model.

Abstract

We study the renormalized energy-momentum tensor of gravitons in a de Sitter space-time. After canonically quantizing only the physical degrees of freedom, we adopt the standard adiabatic subtraction used for massless minimally coupled scalar fields as a regularization procedure and find that the energy density of gravitons in the E(3) invariant vacuum is proportional to H^4, where H is the Hubble parameter, but with a positive sign. According to this result the scalar expansion rate, which is gauge invariant in de Sitter space-time, is increased by the fluctuations. This implies that gravitons may then add to conformally coupled matter in driving the Starobinsky model of inflation.