Stability and superluminality of spherical DBI galileon solutions

TL;DR

This paper investigates spherical solutions in DBI galileon theories, demonstrating their stability and superluminal behavior, which raises questions about their compatibility with standard Lorentz-invariant UV completions.

Contribution

It shows the existence and stability of spherical solutions in DBI galileons and highlights their inherent superluminality, challenging UV completion assumptions.

Findings

Stable spherical solutions exist in certain parameter regions.

Solutions exhibit superluminal propagation.

Superluminality questions Lorentz-invariant UV completion.

Abstract

The DBI galileons are a generalization of the galileon terms, which extend the internal galilean symmetry to an internal relativistic symmetry, and can also be thought of as generalizations of DBI which yield second order field equations. We show that, when considered as local modifications to gravity, such as in the Solar system, there exists a region of parameter space in which spherically symmetric static solutions exist and are stable. However, these solutions always exhibit superluminality, casting doubt on the existence of a standard Lorentz invariant UV completion.