The gauge algebra of double field theory and Courant brackets

Understand

We investigate the symmetry algebra of the recently proposed field theory on a doubled torus that describes closed string modes on a torus with both momentum and winding.

• The gauge parameters are constrained fields on the doubled space and transform as vectors under T-duality.
• The gauge algebra defines a T-duality covariant bracket.
• For the case in which the parameters and fields are T-dual to ones that have momentum but no winding, we find the gauge transformations to all orders and show that the gauge algebra reduces to one obtained by Siegel.