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We have recently proposed an "Ultra-Strong" version of the EquivalencePrinciple (EP) that is not satisfied by standard semiclassical gravity. In thetheory that we are conjecturing, the vacuum expectation value of the (bare)energy momentum tensor is exactly the same as in flat space: quarticallydivergent with the cut-off and with no spacetime dependent (subleading) ter ms.The presence of such terms seems in fact related to some known difficulties,such as the black hole information loss and the cosmological constant problem.Since the terms that we want to get rid of are subleading in the high-momentumexpansion, we attempt to explore the conjectured theory by "IR-completing" GR.We consider a scalar field in a flat FRW Universe and isolate the firstIR-correction to its Fourier modes operators that kills the quadratic (next toleading) time dependent divergence of the stress energy tensor VEV. Analogouslyto other modifications of field operators that have been proposed in theliterature (typically in the UV), the present approach seems to suggest abreakdown (here, in the IR, at large distances) of the metric manifolddescription. We show that corrections to GR are in fact very tiny, becomeeffective at distances comparable to the inverse curvature and do not containany adjustable parameter. Finally, we derive some cosmological implications. Bystudying the consistency of the canonical commutation relations, we infer acorrection to the distance between two comoving observers, which grows as thescale factor only when small compared to the Hubble length, but gets relevantcorrections otherwise. The corrections to cosmological distance measures arealso calculable and, for a spatially flat matter dominated Universe, go in thedirection of an effective positive acceleration.

The IR-Completion of Gravity: What happens at Hubble Scales?