Backreaction from non-conformal quantum fields in de Sitter spacetime

Understand

We study the backreaction on the mean field geometry due to a non-conformal quantum field in a Robertson-Walker background.

• In the regime of small mass and small deviation from conformal coupling, we compute perturbatively the expectation value of the stress tensor of the field for a variety of vacuum states, and use it to obtain explicitly the semiclassical gravity solutions for isotropic perturbations around de Sitter spacetime, which is found to be stable.
• Our results show clearly the crucial role of the non-local terms that appear in the effective action: they cancel the contribution from local terms proportional to the logarithm of the scale factor which would otherwise become dominant at late times and prevent the existence of a stable self-consistent de Sitter solution.
• Finally, the opposite regime of a strongly non-conformal field with a large mass is also considered.