Les Houches Lectures on Physics Beyond the Standard Model of Cosmology

TL;DR

This paper reviews extensions of the standard cosmological model involving additional light dark sector particles, focusing on screening mechanisms that hide deviations from gravity and produce environment-dependent experimental signatures.

Contribution

It provides a comprehensive overview of theoretical models with light dark sector degrees of freedom and their screening mechanisms in cosmology.

Findings

Screening mechanisms effectively hide new fields in the solar system.

Environmental dependence leads to distinctive experimental signatures.

Extensions of the standard model can be consistent with current observations.

Abstract

In these Lectures, I review various extensions of the Lambda-Cold Dark Matter model, characterized by additional light degrees of freedom in the dark sector. In order to reproduce the successful phenomenology of GR in the solar system, these fields must effectively decouple from matter on solar system/laboratory scales. This is achieved through screening mechanisms, which rely on the interplay between self-interactions and coupling to matter to suppress deviations from standard gravity. The manifestation of the new degrees of freedom depends sensitively on their environment, which in turn leads to striking experimental signatures.