Chameleonic Theories: A Short Review

TL;DR

This paper reviews chameleonic theories where scalar fields adapt their mass based on environmental density, covering their mathematical framework, key effects, and extensions to $f(R)$ gravity and quantum gravity.

Contribution

It provides a concise overview of the theoretical aspects of chameleon mechanisms, including their Lagrangian, conformal transformations, and extensions to modified gravity and quantum theories.

Findings

Analysis of the chameleon mechanism's key features

Discussion of $f(R)$ theories and quantum gravity extensions

Clarification of the thin-shell effect and conformal transformations

Abstract

In the chameleon mechanism, a field (typically scalar) has a mass that depends on the matter density of the environment: the larger is the matter density, the larger is the mass of the chameleon. We briefly review some aspects of chameleonic theories. In particular, in a typical class of these theories, we discuss the lagrangian, the role of conformal transformations, the equation of motion and the thin-shell effect. We also discuss $f(R)$ theories and chameleonic quantum gravity.