A Unique Connection for Born Geometry

TL;DR

This paper establishes a unique, torsionless connection in Born geometry, a framework that unifies T-duality and phase space structures in string theory, resolving key ambiguities in double field theory.

Contribution

It proves the existence and uniqueness of a torsionless connection preserving the Born structure, extending the fundamental theorem of Riemannian geometry to this generalized setting.

Findings

Existence of a unique Born connection.

Resolution of ambiguities in double field theory.

Extension of Riemannian geometry principles.

Abstract

It has been known for a while that the effective geometrical description of compactified strings on $d$-dimensional target spaces implies a generalization of geometry with a doubling of the sets of tangent space directions. This generalized geometry involves an $O(d,d)$ pairing $\eta$ and an $O(2d)$ generalized metric $\mathcal{H}$. More recently it has been shown that in order to include T-duality as an effective symmetry, the generalized geometry also needs to carry a phase space structure or more generally a para-Hermitian structure encoded into a skew-symmetric pairing $\omega$. The consistency of string dynamics requires this geometry to satisfy a set of compatibility relations that form what we call a Born geometry. In this work we prove an analogue of the fundamental theorem of Riemannian geometry for Born geometry. We show that there exists a unique connection which preserves the Born structure $(\eta,\omega,\mathcal{H})$ and which is torsionless in a generalized sense. This resolves a fundamental ambiguity that is present in the double field theory formulation of effective string dynamics.