The Shape of Gravity

TL;DR

This paper explores a five-dimensional Anti-de Sitter model with two branes, where gravity appears four-dimensional despite extra dimensions, and discusses implications for collider physics and hierarchy problem solutions.

Contribution

It presents a consistent brane-world scenario with localized gravity and a continuum of gravitational modes, extending previous models with new phenomenological insights.

Findings

Gravity appears four-dimensional up to a position-dependent scale

Light gravitational modes have suppressed couplings

Observable effects similar to six large extra dimensions

Abstract

In a nontrivial background geometry with extra dimensions, gravitational effects will depend on the shape of the Kaluza-Klein excitations of the graviton. We investigate a consistent scenario of this type with two positive tension three-branes separated in a five-dimensional Anti-de Sitter geometry. The graviton is localized on the ``Planck'' brane, while a gapless continuum of additional gravity eigenmodes probe the {\it infinitely} large fifth dimension. Despite the background five-dimensional geometry, an observer confined to either brane sees gravity as essentially four-dimensional up to a position-dependent strong coupling scale, no matter where the brane is located. We apply this scenario to generate the TeV scale as a hierarchically suppressed mass scale. Arbitrarily light gravitational modes appear in this scenario, but with suppressed couplings. Real emission of these modes is observable at future colliders; the effects are similar to those produced by {\it six} large toroidal dimensions.