Palatini Approach Beyond Einstein's Gravity

TL;DR

This paper reviews recent developments in Palatini-formulated extensions of general relativity, highlighting their unique dynamics and applications in quantum gravity, cosmology, and black hole physics.

Contribution

It summarizes the peculiar second-order dynamics of Palatini theories and their potential in addressing quantum gravity phenomenology and singularity resolution.

Findings

Palatini theories have no new degrees of freedom.

They can model nonsingular bouncing cosmologies.

Black hole interiors may develop finite-density cores instead of singularities.

Abstract

I review recent results obtained for extensions of general relativity formulated within the Palatini formalism, an approach in which metric and connection are treated as independent geometrical entities. The peculiar dynamics of these theories, governed by second-order equations and having no new degrees of freedom, makes them specially suitable to address certain aspects of quantum gravity phenomenology, construct nonsingular bouncing cosmologies, and explore black hole interiors, which in the Reissner-Nordstrom case develop a compact core of finite density instead of a point-like singularity.