Duality Beyond the First Loop

TL;DR

This paper calculates two-loop corrections to T-duality in string theory, revealing the crucial role of torsion fields and supporting T-duality as an order-by-order symmetry in the full theory.

Contribution

It provides explicit two-loop $eta$-function corrections to T-duality transformations, emphasizing the importance of torsion fields in the duality map.

Findings

Two-loop corrections depend on torsion fields.

Explicit form of $O(\alpha')$ modifications derived.

T-duality remains a symmetry order-by-order in string tension.

Abstract

In this article we give a calculation of the two-loop $\sigma$-model corrections to the T-duality map in string theory. We use the effective action approach, and analyze two-loop corrections in a specific subtraction scheme. Focusing on backgrounds which have a single Abelian isometry, we find the explicit form for the $O(\alpha')$ modifications of the lowest order duality transformations. Rather surprisingly, the manifest two-loop duality depends crucially on the torsion field. In contrast to the dilaton and metric fields, which are merely passive spectators, the torsion plays a more active role, because of the anomalous couplings to the gauge fields that arise via dimensional reduction. Our results support the interpretation of T-duality as an expansion in the inverse string tension $\alpha'$, and its order-by-order realization as a manifest symmetry of the full string theory.