Notes on the post-Newtonian limit of massive Brans-Dicke theory

TL;DR

This paper investigates the Post-Newtonian limit of massive Brans-Dicke theory, revealing conditions under which a Chameleon-like mechanism can exist in the Jordan frame without contradicting linearization assumptions.

Contribution

It demonstrates that Chameleon-like behavior can occur in the Jordan frame of Brans-Dicke theory at =0, consistent with Post-Newtonian linearization, and clarifies differences from the standard Chameleon mechanism.

Findings

Chameleon-like behavior can exist in the Jordan frame for =0.

Linearization in the Post-Newtonian limit is compatible with a heavy scalar field.

Conditions for Chameleon-like behavior align with small cosmological constant scenarios.

Abstract

We consider the Post-Newtonian limit of massive Brans-Dicke theory and we make some notes about the Post-Newtonian limit of the case $\omega=0$. This case is dynamically equivalent to the metric $f(R)$ theory. It is known that this theory can be compatible with the solar system tests if Chameleon mechanism occurs. Also, it is known that this mechanism is because of the non-linearity in the field equations produced by the largeness of the local curvature relative to the background curvature. Thus, the linearization of the field equations breaks down. On the other hand we know that Chameleon mechanism exists when a coupling between the matter and the scalar field exists. In the Jordan frame of Brans-Dicke theory, we have not such a coupling. But in the Einstein frame this theory behaves like a Chameleon scalar field. By confining ourselves to the case $\omega=0$, we show that "Chameleon-like" behavior can exist also in the Jordan frame but it has an important difference compared with the Chameleon mechanism. Also we show that the conditions which lead to the existence of "Chameleon-like" mechanism are consistent with the conditions in the Post-Newtonian limit which correspond to a heavy scalar filed at the cosmological scale and a small effective cosmological constant. Thus, one can linearize field equations to the Post-Newtonian order and this linearization has not any contradiction with the existence of "Chameleon-like" behavior.