Modified Gravity with a Non-minimal Gravitational Coupling to Matter

TL;DR

This paper explores modified gravity theories with a non-minimal coupling between matter and geometry, analyzing their implications for cosmic acceleration and energy transfer, constrained by thermodynamics and cosmological observations.

Contribution

It introduces a class of gravity models with direct matter-geometry coupling and investigates their cosmological consequences and thermodynamic consistency.

Findings

Coupling leads to non-conservation of matter stress tensor.

Energy transfer occurs from geometry to matter, consistent with thermodynamics.

Such models can explain cosmic acceleration under certain coupling constraints.

Abstract

We consider modified theories of gravity with a direct coupling between matter and geometry, denoted by an arbitrary function in terms of the Ricci scalar. Due to such a coupling, the matter stress tensor is no longer conserved and there is an energy transfer between the two components. By solving the conservation equation, we argue that the matter system should gain energy in this interaction, as demanded by the second law of thermodynamics. In a cosmological setting, we show that although this kind of interaction may account for cosmic acceleration, this latter together with direction of the energy transfer constrain the coupling function.