Wave function of the radion with BPS branes

TL;DR

This paper analyzes the spectrum of coupled gravity and scalar fields in a warped five-dimensional setup with BPS branes, revealing two massless modes and massive KK excitations, and deriving the effective 4D tensor-scalar action.

Contribution

It provides a complete tensor-scalar spectrum and effective action for a warped AdS_5 model with BPS branes and special scalar potentials, without stabilizing the orbifold size.

Findings

Two massless scalar zero modes identified: radion and dilaton.

Scalar KK modes have masses around the warped mass scale.

The 4D effective action is of tensor-scalar type.

Abstract

We investigate coupled gravity and a bulk scalar field on a slice of AdS_5 bulk with special BPS branes at the two ends. With the special scalar potentials on the branes the scalar field does not stabilize the size of the orbifold. With a careful treatment of the general coordinate invariance the complete tensor-scalar spectrum is presented. There are two massless zero modes in the scalar sector, the radion and a dilatonic zero mode. The scalar KK modes acquire masses at the order of the warped mass scale. The four dimensional effective action is of tensor-scalar type.