Bulk Fields in Dilatonic and Self-Tuning Flat Domain Walls

TL;DR

This paper investigates the behavior of zero modes of massless bulk fields in dilatonic and self-tuning flat domain walls, revealing normalizability and effective gravity compactification, but also unexpected non-vanishing cosmological constant in self-tuning cases.

Contribution

It demonstrates the normalizability of zero modes in dilatonic domain walls and analyzes the effective gravity, highlighting issues with the cosmological constant in self-tuning flat domain walls.

Findings

Zero modes are normalizable in dilatonic domain walls.

Gravity effectively reduces to Einstein gravity with zero cosmological constant in dilatonic cases.

Self-tuning flat domain walls exhibit a non-zero cosmological constant in the effective theory.

Abstract

We study the Kaluza-Klein zero modes of massless bulk fields with various spins in the background of dilatonic and self-tuning flat domain walls. We find that the zero modes of all the massless bulk fields in such domain wall backgrounds are normalizable, unlike those in the background of the non-dilatonic domain wall with infinite extra space of Randall and Sundrum. In particular, gravity in the bulk of dilatonic domain walls is effectively compactified to the Einstein gravity with vanishing cosmological constant and nonzero gravitational constant in one lower dimensions for any values of dilaton coupling parameter, provided the warp factor is chosen to decrease on both sides of the domain wall, in which case the tension of the domain wall is positive. However, unexpectedly, for the self-tuning flat domain walls, the cosmological constant of the zero mode effective gravity action in one lower dimensions does not vanish, indicating the need for additional ingredient or modification necessary in cancellation of the unexpected cosmological constant in the graviton zero mode effective action.