Close to the edge: hierarchy in a double braneworld

TL;DR

This paper demonstrates how a double thick-brane in an AdS5 spacetime can naturally generate the hierarchy between the Planck and weak scales by localizing gravitons and fermions at different edges, with implications for gravity and particle physics.

Contribution

It introduces a stable BPS double-wall solution in AdS5 that localizes gravitons and fermions at separate edges, providing a geometric explanation for the hierarchy problem.

Findings

Graviton zero-mode is exponentially suppressed at the fermion edge.

Massive modes decouple, restoring Newtonian gravity.

Fermions are localized at one edge due to lack of reflection symmetry.

Abstract

We show that the hierarchy between the Planck and the weak scales can follow from the tendency of gravitons and fermions to localize at different edges of a thick double wall embedded in an $AdS_5$ spacetime without reflection symmetry. This double wall is a stable BPS thick-wall solution with two sub-walls located at its edges; fermions are coupled to the scalar field through Yukawa interactions, but the the lack of reflection symmetry forces them to be localized in one of the sub-walls. We show that the graviton zero-mode wavefunction is suppressed in the fermion edge by an exponential function of the distance between the sub-walls, and that the massive modes decouple so that Newtonian gravity is recuperated.