The post-Newtonian limit in C-theories of gravitation

TL;DR

This paper develops a method to compute PPN parameters in C-theories of gravity, revealing that some models with long-distance modifications can still pass Solar System tests, thus broadening the scope of viable alternative gravity theories.

Contribution

It provides a systematic way to calculate PPN parameters in C-theories and nonminimally coupled curvature theories, correcting earlier inaccuracies in the literature.

Findings

Certain models with long-distance modifications pass Solar System tests

Corrected previous calculations of PPN parameters in nonminimally coupled theories

Established a unified framework for PPN analysis in various gravity theories

Abstract

C-theory provides a unified framework to study metric, metric-affine and more general theories of gravity. In the vacuum weak-field limit of these theories, the parameterized post-Newtonian (PPN) parameters $\beta$ and $\gamma$ can differ from their general relativistic values. However, there are several classes of models featuring long-distance modifications of gravity but nevertheless passing the Solar system tests. Here it is shown how to compute the PPN parameters in C-theories and also in nonminimally coupled curvature theories, correcting previous results in the literature for the latter.