Soft gravitational effects in Kadanoff-Baym approach

Understand

In de Sitter space, the gravitational fluctuation at the super-horizon scale may make physical quantities time dependent by breaking the de Sitter symmetry.

• We adopt the Kadanoff-Baym approach to evaluate soft gravitational effects in a matter system at the sub-horizon scale.
• This investigation proves that only the local terms contribute to the de Sitter symmetry breaking at the one-loop level.
• The IR singularities in the non-local terms cancel after summing over degenerate states between real and virtual processes.