Shortcuts in the fifth dimension

TL;DR

This paper investigates how gravitational signals can take shortcuts through a fifth dimension in a brane-world universe, potentially affecting cosmological observations by allowing gravity to propagate faster than light along the brane.

Contribution

It quantifies the effect of fifth-dimensional shortcuts on gravitational signal propagation and explores their implications for cosmology.

Findings

Gravitational signals can travel faster via shortcuts in the bulk.

Shortcuts can lead to observable differences in gravitational versus luminous signals.

Impacts on cosmological models and potential observational signatures.

Abstract

If our Universe is a three-brane embedded in a five-dimensional anti-deSitter spacetime, in which matter is confined to the brane and gravity inhabits an infinite bulk space, then the causal propagation of luminous and gravitational signals is in general different. A gravitational signal traveling between two points on the brane can take a ``shortcut'' through the bulk, and appear quicker than a photon traveling between the same two points along a geodesic on the brane. Similarly, in a given time interval, a gravitational signal can propagate farther than a luminous signal. We quantify this effect, and analyze the impact of these shortcuts through the fifth dimension on cosmology.