High frequency limit for gravitational perturbations of cosmological models in modified gravity theories

Understand

In general relativity, it has been shown that the effective gravitational stress-energy tensor for short-wavelength metric perturbations acts just like that for a radiation fluid, and thus, in particular, cannot provide any effects that mimic dark energy.

• However, it is far from obvious if this property of the effective gravitational stress-energy tensor is a specific nature held only in the Einstein gravity, or holds also in other theories of gravity.
• In particular, when considering modified gravity theories that involve higher order derivative terms, one may expect to have some non-negligible effects arising from higher order derivatives of short-wavelength perturbations.
• In this paper, we argue this is not the case at least in the cosmological context.