Approaches to Understanding Cosmic Acceleration

TL;DR

This paper reviews theoretical approaches to explaining cosmic acceleration, including the cosmological constant, dark energy, and modifications to general relativity, discussing their implications and challenges.

Contribution

It provides a comprehensive overview of three main theoretical frameworks for cosmic acceleration, highlighting their problems and potential origins.

Findings

Cosmological constant faces fine-tuning issues.

Dark energy models encounter fundamental physics challenges.

Infrared modifications to gravity offer alternative explanations.

Abstract

Theoretical approaches to explaining the observed acceleration of the universe are reviewed. We briefly discuss the evidence for cosmic acceleration, and the implications for standard General Relativity coupled to conventional sources of energy-momentum. We then address three broad methods of addressing an accelerating universe: the introduction of a cosmological constant, its problems and origins; the possibility of dark energy, and the associated challenges for fundamental physics; and the option that an infrared modification of general relativity may be responsible for the large-scale behavior of the universe.