Green-Schwarz mechanism and α′-deformed Courant brackets

We establish that the unusual two-form gauge transformations needed in the Green-Schwarz anomaly cancellation mechanism fit naturally into an α′-deformed generalized geometry. The algebra of gauge transformations is a consistent deformation of the Courant bracket and features a nontrivial modification of the diffeomorphism group. This extension of generalized geometry emerged from a ‘doubled α′-geometry’, which provides a construction of exactly gauge and T-duality invariant α′ corrections to the effective action.