Aspects of Infrared Non-local Modifications of General Relativity

TL;DR

This thesis explores infrared non-local modifications to General Relativity as a potential explanation for dark energy, analyzing their theoretical consistency and observational viability.

Contribution

It introduces new non-local gravity models inspired by massive gravity that preserve diffeomorphism symmetry and examines their cosmological implications.

Findings

Models can explain accelerated expansion without dark energy.

Some models are consistent with observational constraints.

Addressed stability issues in non-local field theories.

Abstract

In this thesis we are interested in the problem of dark energy in cosmology. In particular, we consider the possibility that this effect is due to an infrared non-local modification of the theory of General Relativity. Inspired by massive gravity, we construct non-local theories in which gravity may be massive, but where the symmetry of diffeomorphisms is preserved. We focus on the cosmology of these theories and confront them with observational constraints. On a more theoretical level, we discuss some subtleties of non-local field theory and address in a novel way the issue of stability. This thesis is based on both published and original work.