Superluminal Propagation on a Moving Braneworld

TL;DR

This paper explores how a moving brane in a higher-dimensional space can exhibit superluminal propagation of bulk fields, breaking Lorentz symmetry and potentially impacting cosmological observations.

Contribution

It demonstrates that brane motion can lead to superluminal bulk field propagation, revealing Lorentz symmetry breaking in a simple braneworld model.

Findings

Bulk fields can propagate outside the brane lightcone when the brane is in motion.

Superluminal effects are parametrically large, set by brane velocity.

Potential observational tests and cosmological applications are discussed.

Abstract

We consider a braneworld scenario in the simplest setting, $M_4 \times S^1$, with a 4D Minkowski metric induced on the brane, and establish the possibility of superluminal propagation. If the brane is at rest, the 4D Lorentz symmetry of the brane is exact, but if the brane is in motion, it is broken globally by the compactification. By measuring bulk fields, an observer on the brane sees a slice through a higher-dimensional field profile, which carries an imprint of the extra dimensions even when the brane is at rest. If the brane is in motion we find that bulk fields can propagate outside the brane lightcone by a parametrically large amount set by the brane velocity. We mention observational tests and possible applications to cosmology.