Closed Timelike Curves in the Galileon Model

TL;DR

This paper demonstrates the existence of closed timelike curves in the Galileon model, showing that certain solutions admit CTCs when higher derivative terms dominate, highlighting potential causality issues in these theories.

Contribution

It provides the first explicit solution in the Galileon model that admits closed timelike curves, revealing new causality considerations.

Findings

Solutions with CTCs exist in the Galileon model

CTCs occur when higher derivative terms dominate

Implications for causality in modified gravity theories

Abstract

It has long been known that generic solutions to the nonlinear DGP and Galileon models admit superluminal propagation. In this note we present a solution of these models which also admits closed timelike curves (CTCs). We observe that these CTCs only arise when, according to each observer, there exists some region in which the higher derivative terms are larger than the 2-derivative kinetic term.