Avoiding the dangers of a soft-wall singularity

TL;DR

This paper critically examines the infrared singularity in Randall-Sundrum soft-wall models, showing that the singularity can satisfy boundary conditions without requiring a black-hole horizon, challenging previous assumptions about its nature.

Contribution

It demonstrates that the infrared singularity in soft-wall models can satisfy unitary boundary conditions without the need for a black-hole horizon, offering a new perspective on singularity shielding.

Findings

The singularity can satisfy unitary boundary conditions.

Shielding by a black-hole horizon is not necessary.

The spectrum of 4D states remains similar to the original soft-wall case.

Abstract

We critically analyse the nature of the infrared singularity in Randall-Sundrum soft-wall models, where the extra dimension is dynamically compactified by the formation of a curvature singularity. Due to the Israel junction conditions, this singularity can only be shielded by a time-independent black-hole horizon if there is ghost matter on the UV brane. For this construction the spectrum of 4D states is shown to be similar to the original soft-wall case. We point out, however, that no such shielding is needed, as the singularity satisfies unitary boundary conditions.