Flux quantization in dilatonic Taub-NUT dyons

TL;DR

This paper explores how topological properties of spacetimes with boundaries influence flux quantization of fields in dilatonic Taub-NUT backgrounds, revealing flux quanta for axion and dilaton fields linked to string theory.

Contribution

It demonstrates the topological origin of flux quantization for axion and dilaton fields in Taub-NUT spacetimes within heterotic string theory, using homology and cohomology methods.

Findings

Electromagnetic fluxes are topologically unrestricted.

Axion and dilaton fluxes are quantized due to topological charges.

Results connect flux quantization to string theory bundle structures.

Abstract

Spacetimes that include a boundary at infinity have a non-trivial topology. The homology of the background influences gauge fields living on them and lead to topological charges. We investigate the charges and fluxes of fields over a Taub--NUT background in Einstein--Maxwell dilaton--axion gravity, by using the relative homology and de Rham cohomology. It turns out that the electromagnetic sector is devoid of restrictions from a topological viewpoint. There are, however, flux quanta for the axion and dilaton fields. These results are obtained from the absolute homology of the spacetime boundary. The solutions we probe originate in the four dimensional low energy limit of heterotic string theory. So our results are complemented by the stringy coupling present in the fields. The quantization has a bundle theoretic interpretation as the axion's flux corresponds to the topological index of an underlying 2-bundle.