Modified gravity with R-matter couplings and (non-)geodesic motion

TL;DR

This paper explores alternative gravity theories with matter-Ricci scalar couplings, analyzing their relation to scalar-tensor theories, effects on matter motion, and potential to address galaxy dark matter issues.

Contribution

It introduces and examines gravity models with direct matter-Ricci scalar couplings, highlighting their impact on matter motion and the dark matter problem in galaxies.

Findings

Matter motion can be non-geodesic in these theories

Potential to explain galaxy rotation curves without dark matter

Implications for the Equivalence Principle

Abstract

We consider alternative theories of gravity with a direct coupling between matter and the Ricci scalar We study the relation between these theories and ordinary scalar-tensor gravity, or scalar-tensor theories which include non-standard couplings between the scalar and matter. We then analyze the motion of matter in such theories, its implications for the Equivalence Principle, and the recent claim that they can alleviate the dark matter problem in galaxies.