Strong/Weak Coupling Duality from the Dual String

TL;DR

This paper explores the duality between fundamental and solitonic strings in compactified string theories, revealing a strong/weak coupling duality and mechanisms for gauge symmetry enhancement in four-dimensional models.

Contribution

It demonstrates how dual strings in six and four dimensions exhibit a target-space duality containing the axion-dilaton SL(2,Z), providing insights into non-perturbative effects and gauge symmetry.

Findings

Identification of a dual string with an $O(2,2;Z)$ duality group.

Establishment of a strong/weak coupling duality via the axion-dilaton $SL(2,Z)$.

Proposal of a new non-perturbative gauge symmetry enhancement mechanism.

Abstract

On compactification to six spacetime dimensions, the fundamental heterotic string admits as a soliton a dual string whose effective worldsheet action couples to the background fields of the dual formulation of six-dimensional supergravity. On further toroidal compactification to four spacetime dimensions, the dual string acquires an $O(2,2;Z)$ target-space duality. This contains as a subgroup the axion-dilaton $SL(2,Z)$ which corresponds to a strong/weak coupling duality for the fundamental string. The dual string also provides a new non-perturbative mechanism for enhancement of the gauge symmetry.