Acceleration from Modified Gravity: Lessons from Worked Examples

TL;DR

This paper explores how specific modified gravity models, like f(R) and DGP, inform our understanding of distinguishing modified gravity from dark energy and addressing non-linear dynamics in cosmological tests.

Contribution

It provides detailed analysis of two modified gravity models to address key challenges in testing gravity through cosmological observations.

Findings

Insights into parameterizing deviations from general relativity.

Understanding of non-linear effects in modified gravity models.

Guidance on distinguishing modified gravity from dark energy.

Abstract

I examine how two specific examples of modified gravity explanations of cosmic acceleration help us understand some general problems confronting cosmological tests of gravity: how do we distinguish modified gravity from dark energy if they can be made formally equivalent? how do we parameterize deviations according to physical principles with sufficient generality, yet focus cosmological tests into areas that complement our existing knowledge of gravity? how do we treat the dynamics of modifications which necessarily involve non-linearities that preclude superposition of forces? The modified action f(R) and DGP braneworld models provide insight on these question as fully-worked examples whose expansion history, linear perturbation theory, and most recently, non-linear N-body and force-modification field dynamics of cosmological simulations are available for study.