Theoretical Aspects of Cosmic Acceleration

TL;DR

This paper reviews theoretical constraints on models explaining the universe's late-time acceleration, emphasizing the importance of consistency conditions and illustrating with the Galileon model and its Vainshtein mechanism.

Contribution

It provides a comprehensive overview of the theoretical aspects and constraints of various cosmic acceleration models, highlighting recent ideas and the Galileon model as a case study.

Findings

Constraints from theoretical consistency limit model parameters.

The Vainshtein mechanism effectively screens modifications in the Galileon model.

Theoretical issues arise around certain background solutions.

Abstract

Efforts to understand and map the possible explanations for the late time acceleration of the universe have led to a broad range of suggestions, ranging from the cosmological constant and straightforward dark energy, to exotically coupled models, to infrared modifications of General Relativity. If we are to uncover which, if any, of these approaches might provide a serious answer to the problem, it is crucial to understand the constraints that theoretical consistency places on the models, and on the regimes in which they make predictions. In this talk, delivered as an invited plenary lecture at the Dark Side of the Universe conference in Kyoto, Japan, I briefly describe some modern attempts to carry out this program and some of the more interesting ideas that have emerged. As an example, I use the Galileon model, discussing how the Vainshtein mechanism occurs, and how a number of these theoretical problems arise around such backgrounds.