Hybrid modified gravity unifying local tests, galactic dynamics and late-time cosmic acceleration

TL;DR

This paper explores hybrid metric-Palatini gravity, a unified framework that can explain local tests, galactic dynamics, and cosmic acceleration by introducing a light scalar field affecting multiple scales.

Contribution

It introduces and analyzes a hybrid gravity model combining metric and Palatini formalisms, providing a unified approach to dark energy and dark matter phenomena.

Findings

The theory predicts a light scalar field compatible with local constraints.

It can account for galactic rotation curves without dark matter.

It offers a potential explanation for late-time cosmic acceleration.

Abstract

The non-equivalence between the metric and Palatini formalisms of $f(R)$ gravity is an intriguing feature of these theories. However, in the recently proposed hybrid metric-Palatini gravity, consisting of the superposition of the metric Einstein-Hilbert Lagrangian with an $f(\cal R)$ term constructed \`{a} la Palatini, the "true" gravitational field is described by the interpolation of these two non-equivalent approaches. The theory predicts the existence of a light long-range scalar field, which passes the local constraints and affects the galactic and cosmological dynamics. Thus, the theory opens new possibilities for a unified approach, in the same theoretical framework, to the problems of dark energy and dark matter, without distinguishing a priori matter and geometric sources, but taking their dynamics into account under the same standard.