String and Fivebrane Solitons: Singular or Non-singular?

TL;DR

This paper investigates whether superstring and superfivebrane solutions in D=10 supergravity can be interpreted as non-singular solitons, revealing that singularity nature depends on the probe used, with some configurations appearing non-singular.

Contribution

It introduces a probe/source approach to analyze the singularities of superstring and superfivebrane solutions, showing their singularity status depends on the probe configuration.

Findings

Singularities are probe-dependent; real when probe and source are the same.

Superstring and superfivebrane solutions can be non-singular under certain conditions.

Black strings and fivebranes always have genuine singularities.

Abstract

We ask whether the recently discovered superstring and superfivebrane solutions of D=10 supergravity admit the interpretation of non-singular solitons even though, in the absence of Yang-Mills fields, they exhibit curvature singularities at the origin. We answer the question using a test probe/source approach, and find that the nature of the singularity is probe-dependent. If the test probe and source are both superstrings or both superfivebranes, one falls into the other in a finite proper time and the singularity is real, whereas if one is a superstring and the other a superfivebrane it takes an infinite proper time (the force is repulsive!) and the singularity is harmless. Black strings and fivebranes, on the other hand, always display real singularities.