Galileons in the Sky

TL;DR

Galileon theories provide a unifying framework for infrared modifications of gravity that screen fifth forces and drive cosmological evolution. The paper surveys how Galileon-like scalars arise in DGP, New Massive Gravity, and ghost-free massive gravity, and explains their non-renormalization properties that protect the EFT from large quantum corrections. It then discusses cosmological applications, including self-acceleration, degravitating solutions, and Galileon inflation, highlighting observational signatures such as altered lensing and distinctive non-Gaussianities. Overall, the work emphasizes theoretical consistency of ghost-free constructions and outlines challenges and directions for connecting Galileon physics to late-time acceleration and early-Universe inflation.

Abstract

We review the different frameworks in which Galileon scalar fields have been seen to emerge such an in DGP, New Massive Gravity and Ghost-free massive Gravity and emphasize their relation with the Lovelock invariant in braneworld models. The existence of a non-renormalization theorem for Galileon scalar fields makes them especially attractive candidates for inflation as well as for late-time acceleration. In particular we review the self-accelerating and degravitating branches of solutions present in Galileon models when arising from Massive Gravity and discuss their phenomenology.