Nonlocal Galileons and Self-Acceleration

TL;DR

This paper introduces nonlocal Galileons derived from theories that eliminate the cosmological constant, showing they can lead to stable, self-accelerating solutions in massive gravity with improved perturbative stability.

Contribution

It develops a new class of nonlocal Galileons that modify massive gravity, enabling stable self-accelerating cosmological solutions with better fluctuation stability.

Findings

Nonlocal Galileons eliminate the cosmological constant from the theory.

Stable, self-accelerated solutions are found with nonlocal terms.

Perturbations are stable and non-superluminal under certain parameters.

Abstract

A certain class of nonlocal theories eliminates an arbitrary cosmological constant (CC) from a universe that can be perceived as our world. Dark energy then cannot be explained by a CC; it could however be due to massive gravity. We calculate the new corrections, which originate from the nonlocal terms that eliminate the CC, to the decoupling limit Lagrangian of massive gravity. The new nonlocal terms also have internal field space Galilean symmetry and are referred here as "nonlocal Galileons." We then study a self-accelerated solution and show that the new nonlocal terms change the perturbative stability analysis. In particular, small fluctuations are now stable and non-superluminal for some simple parameter choices, whereas for the same choices the pure massive gravity fluctuations are unstable. We also study stable spherically symmetric solutions on this background.