Dark Energy vs. Modified Gravity

TL;DR

This paper reviews the distinctions between Dark Energy and Modified Gravity models in explaining the universe's accelerated expansion, focusing on their theoretical foundations and observable signatures.

Contribution

It provides a clear classification and phenomenological overview of Dark Energy and Modified Gravity models, emphasizing their fundamental differences based on equivalence principles.

Findings

Differentiates Dark Energy from Modified Gravity using equivalence principles

Summarizes observable signatures for both categories

Highlights the theoretical and phenomenological distinctions

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.