Some Aspects of the T-Duality Symmetric String Sigma Model

TL;DR

This paper presents a T-duality symmetric string sigma model that explicitly includes dual coordinates, explores its geometric and symmetry properties, and discusses its quantization and background constraints.

Contribution

It introduces a manifestly T-dual invariant formulation of bosonic string theory with explicit dual coordinates and analyzes its geometric structure and symmetry properties.

Findings

The model exhibits a loss of local Lorentz invariance, recoverable on-shell.

Double torus geometry with $O(D,D)$ invariance arises in constant backgrounds.

Conditions for $O(D,D)$ invariance in non-constant backgrounds are identified.

Abstract

A manifestly T-dual invariant formulation of bosonic string theory is discussed here. It can be obtained by making both the usual string compact coordinates and their duals explicitly appear, on the same footing, in the world-sheet action. A peculiarity of such a model is the loss of the local Lorentz invariance which is required to be recovered on-shell. This dictates a constraint on the backgrounds which characterizes the double geometry of the target space. Constant and non-constant backgrounds are considered. In the former case, the local Lorentz constraint implies the geometry of a double torus with an $O(D,D)$ invariance. In the latter, it is shown how and when the $O(D,D)$ invariance still holds and when deformations from it can be implied. Results of the quantization of the free theory are also briefly exhibited.