Long distance modifications of gravity in four dimensions

TL;DR

This paper explores modifications to four-dimensional gravity that involve additional scalar fields, which can change behavior depending on the environment, potentially affecting cosmic and local gravitational phenomena.

Contribution

It analyzes the properties of scalar-tensor modifications of gravity, highlighting the chameleon-like behavior of extra scalar degrees of freedom in different regimes.

Findings

Presence of at least one light scalar on cosmic scales.

Scalar field can become heavy near mass sources, screening modifications.

Implications for low curvature regimes and gravitational experiments.

Abstract

We discuss some general characteristics of modifications of the 4D Einstein-Hilbert action that become important for low space-time curvatures. In particular we focus on the chameleon-like behaviour of the massive gravitational degrees of freedom. Generically there is at least one extra scalar that is light on cosmic scales, but for certain models it becomes heavy close to any mass source.