Brane gravity, higher derivative terms and non-locality

TL;DR

This paper extends the understanding of weak gravity in brane world models to higher energies, showing it resembles higher derivative gravity and discussing implications for inflation and non-locality.

Contribution

It demonstrates that brane world gravity at high energies mimics higher derivative gravity and explores the emergence of additional fields and non-locality without quantum theory.

Findings

Weak gravity on branes is akin to higher derivative gravity.

The effective 4D action includes curvature-squared terms with some ambiguity.

Higher derivative terms suggest an inherent non-locality in brane scenarios.

Abstract

In brane world scenarios with a bulk scalar field between two branes it is known that 4-dimensional Einstein gravity is restored at low energies on either brane. By using a gauge-invariant gravitational and scalar perturbation formalism we extend the theory of weak gravity in the brane world scenarios to higher energies, or shorter distances. We argue that weak gravity on either brane is indistinguishable from 4-dimensional higher derivative gravity, provided that the inter-brane distance (radion) is stabilized, that the background bulk scalar field is changing near the branes and that the background bulk geometry near the branes is warped. This argument holds for a general conformal transformation to a frame in which matter on the branes is minimally coupled to the metric. In particular, Newton's constant and the coefficients of curvature-squared terms in the 4-dimensional effective action are determined up to an ambiguity of adding a Gauss-Bonnet topological term. In other words, we provide the brane-world realization of the so called $R^2$-model without utilizing a quantum theory. We discuss the appearance of composite spin-2 and spin-0 fields in addition to the graviton on the brane and point out a possibility that the spin-0 field may play the role of an effective inflaton to drive brane-world inflation. Finally, we conjecture that the sequence of higher derivative terms is an infinite series and, thus, indicates non-locality in the brane world scenarios.