Talk by Yashar Akrami (Lorentz Institute in Leiden).
Title: Nonlocal modification of gravity in the infrared: theoretical viability and cosmological constraints
Abstract: Most extensions and modifications of general relativity (GR) are based on the principle of locality, as is GR itself. However, although it is believed to be problematic in fundamental descriptions of nature, one should not exclude the appearance of nonlocalities in effective descriptions of gravity. In particular, such effective nonlocalities appear generically and naturally on ultra-large (or infrared) scales as the remnant of massless/light degrees of freedom integrated out in an otherwise local theory. This provides an interesting framework to describe the evolution of the Universe on the largest scales and to explain the late-time cosmic acceleration. In this talk I will briefly review the idea of nonlocality, theoretical motivations behind it, state-of-the-art nonlocal models and their cosmological implications, as well as current observational constraints. I will then discuss the prospects for further progress along the road of building nonlocal models of gravity and their cosmological tests.