Consistent cosmological modifications to the Einstein equations

TL;DR

This paper proposes a general, covariant framework for modifying Einstein's equations to test gravity on cosmological scales, ensuring consistency with underlying field theories and analyzing implications for cosmic microwave background observations.

Contribution

It introduces a systematic scheme for consistent modifications to Einstein's equations with explicit links to underlying fields, applied to CMB observations.

Findings

Framework connects modifications to field content

Exact Lambda-CDM background maintained

Impacts on CMB fluctuations analyzed

Abstract

General Relativity (GR) is a phenomenologically successful theory that rests on firm foundations, but has not been tested on cosmological scales. The advent of dark energy (and possibly even the requirement of cold dark matter), has increased the need for testing modifications to GR, as the inference of such otherwise undetected fluids, depends crucially on the theory of gravity. In this work I outline a general scheme for constructing consistent and covariant modifications to the Einstein equations. This framework is such that there is a clear connection between the modification and the underlying field content that produces it. I conclude by a simple metric based modification of the fluctuation equations for which the background is exact Lambda-CDM and present its impact on observations of the cosmic microwave background radiation.