Dark Energy vs. Modified Gravity

Abstract

Understanding the reason for the observed accelerated expansion of the Universe represents one of the fundamental open questions in physics. In cosmology, a classification has emerged among physical models for the acceleration, distinguishing between Dark Energy and Modified Gravity. In this review, we give a brief overview of models in both categories as well as their phenomenology and characteristic observable signatures in cosmology. We also introduce a rigorous distinction between Dark Energy and Modified Gravity based on the strong and weak equivalence principles.

Comments: 29 pages, 4 figures; invited review submitted to Annual Reviews of Nuclear and Particle Science; v2: some pertinent references added; v3: table with constraints added, reflects published version; v4 [trivial]: fixed missing references in arxiv version