On the Covariant Galileon and a consistent self-accelerating Universe

TL;DR

This paper explores the connection between flat space Galilean theories and scalar theories coupled to gravity, discussing their invariance, supersymmetry, and implications for self-accelerating cosmological models.

Contribution

It demonstrates that quartic Galileons emerge from non-minimally coupled scalar theories in the decoupling limit and discusses their role in DGP-like models with self-acceleration.

Findings

Galilean theories are recovered in the decoupling limit of Slotheonic theories.

Galilean supersymmetry may only exist within supergravity frameworks.

Quartic and cubic Galileons in DGP models cannot be decoupled.

Abstract

In this paper we show that the flat space Galilean theories with up to three scalars in the equation of motion (the quartic Galileons) are recovered in the decoupling limit of certain scalar theories non-minimally coupled to gravity, the so-called "Slotheonic" theories. These theories are also invariant under the generalized Galilean shifts in curved spacetime. While Galilean self-(derivative)couplings are not explicit in the action, they appear after integrating out gravity. We then argue that Galilean supersymmetric theories may only be found in the context of supergravity. Finally, we discuss on the possibility that Slotheonic theories are the effective four dimensional theories of consistent DGP-like models with self-accelerating cosmological solutions. Moreover, we show that the quartic and cubic Galileon in consistent DGP models cannot be decoupled.