"Detuned" f(R) gravity and dark energy

TL;DR

This paper explores a modified f(R) gravity model with an explicit scalar field coupling, proposing a new approach to explain cosmic acceleration while satisfying local gravity tests.

Contribution

It introduces a detuned f(R) gravity framework with an explicit scalar-matter coupling, expanding the class of scalar-tensor theories for dark energy modeling.

Findings

The detuned model can mimic dark energy effects without conflicting with local gravity constraints.

Scalar field coupling varies with matter density, enabling chameleon-like screening.

The approach offers a new avenue for gravitational explanations of cosmic acceleration.

Abstract

In gravity theories derived from a f(R) Lagrangian, matter is usually supposed to be minimally coupled to the metric, which hence defines a ``Jordan frame.'' However, since the field equations are fourth order, gravity possesses an extra degree of freedom on top of the standard graviton, as is manifest from its equivalent description in the conformally related, Einstein, frame. We introduce explicitly this extra scalar degree of freedom in the action and couple it to matter, so that the original metric no longer defines a Jordan frame. This ``detuning'' puts f(R) gravity into a wider class of scalar--tensor theories. We argue that a ``chameleon-like'' detuning tracing the background matter density may provide purely gravitational models which account for the present acceleration of the universe and evade local gravity constraints.