Hybrid metric-Palatini gravity

TL;DR

This paper reviews hybrid metric-Palatini gravity, a modified gravity theory combining elements of metric and Palatini formalisms, which aims to explain cosmic acceleration and dark matter phenomena without dark energy or dark matter.

Contribution

It introduces and discusses the formulation and successes of the hybrid metric-Palatini gravity approach in addressing cosmological and astrophysical challenges.

Findings

Successfully passes local gravitational tests

Provides a unified framework for dark energy and dark matter

Addresses self-accelerated cosmic expansion

Abstract

Recently, the phenomenology of f(R) gravity has been scrutinized motivated by the possibility to account for the self-accelerated cosmic expansion without invoking dark energy sources. Besides, this kind of modified gravity is capable of addressing the dynamics of several self-gravitating systems alternatively to the presence of dark matter. It has been established that both metric and Palatini versions of these theories have interesting features but also manifest severe and different downsides. A hybrid combination of theories, containing elements from both these two formalisms, turns out to be also very successful accounting for the observed phenomenology and is able to avoid some drawbacks of the original approaches. This article reviews the formulation of this hybrid metric-Palatini approach and its main achievements in passing the local tests and in applications to astrophysical and cosmological scenarios, where it provides a unified approach to the problems of dark energy and dark matter.