Shortcuts in Cosmological Branes

TL;DR

This paper explores gravitational shortcuts in brane-world cosmologies, showing that gravitons can take faster paths than photons, potentially impacting early universe phenomena like inflation and the horizon problem.

Contribution

It demonstrates the existence of gravitational shortcuts in brane-world models and discusses their potential effects on cosmological scenarios.

Findings

Shortcuts exist for gravitons leaving and returning to the brane.

Shortcuts are small in late universes but significant in primordial universes.

Potential corrections to inflationary models and the horizon problem are identified.

Abstract

We aim at gathering information from gravitational interaction in the Universe, at energies where quantum gravity is required. In such a setup a dynamical membrane world in a space-time with scalar bulk matter described by domain walls, as well as a dynamical membrane world in empty Anti de Sitter space-time are analysed. We later investigate the possibility of having shortcuts for gravitons leaving the membrane and returning subsequently. In comparison with photons following a geodesic inside the brane, we verify that shortcuts exist. For late time universes they are small, but for some primordial universes they can be quite effective. In the case of matter branes, we argue that at times just before nucleosynthesis the effect is sufficiently large to provide corrections to the inflationary scenario, especially as concerning the horizon problem and the Cosmological Background Radiation.