T-Duality Can Fail

TL;DR

This paper demonstrates that T-duality, a fundamental symmetry in string theory, can be broken by nonperturbative effects, especially in cases with reduced supersymmetry, challenging previous assumptions about its universality.

Contribution

It provides a detailed analysis showing T-duality can fail due to nonperturbative effects in certain compactifications, and offers a holonomy argument explaining the conditions for T-duality and U-duality.

Findings

T-duality can be broken by nonperturbative effects in specific compactifications.

Holonomy arguments indicate T-duality requires large supersymmetry.

Classical modular symmetry of the 2-torus can also be broken.

Abstract

We show that T-duality can be broken by nonperturbative effects in string coupling. The T-duality in question is that of the 2-torus when the heterotic string is compactified on K3 x T2. This case is compared carefully to a situation where T-duality appears to work. A holonomy argument is presented to show that T-dualities (and general U-dualities) should only be expected for large amounts of supersymmetry. This breaking of R <-> 1/R symmetry raises some interesting questions in string theory which we discuss. Finally we discuss how the classical modular group of a 2-torus appears to be broken too.