Modifications of gravity

Modifications of gravity.

General relativity (GR) is a phenomenologically successful theory that rests on firm foundations, but has not been tested on cosmological scales. The deep mystery of dark energy (and possibly even the requirement of cold dark matter (CDM)) has increased the need for testing modifications to GR, as the inference of such otherwise undetected fluids depends crucially on the theory of gravity. Here...

Teleparallel gravity and its modifications

The teleparallel equivalent of general relativity is an intriguing alternative formulation of general relativity. In this thesis, we examine theories of teleparallel gravity in detail, and explore their relation to a whole spectrum of alternative gravitational models, discussing their position within the hierarchy of Metric Affine Gravity models. Consideration of alternative gravity models is m...

Nonlocal action for long - distance modifications of gravity theory

We construct the covariant nonlocal action for recently suggested long-distance modifications of gravity theory motivated by the cosmological constant and cos-mological acceleration problems. This construction is based on the special non-local form of the Einstein-Hilbert action explicitly revealing the fact that this action within the covariant curvature expansion begins with curvature-squared...

Long distance modifications of gravity in four dimensions.

Models of this kind have been proposed as a way to generate late time acceleration without a cosmological constant1. For this to work the crossover scale has to be of the order of today’s Hubble constant: μ ∼ H0. In the Friedmann equation obtained for these theories, the modification then only becomes important at the present stage of the expansion of the Universe. Obviously the detailed predic...

Avoiding Dark Energy with 1/R Modifications of Gravity