Three-point functions in duality-invariant higher-derivative gravity

Doubled α′-geometry is the simplest higher-derivative gravitational theory with exact global duality symmetry. we use the double metric formulation of this theory to compute on-shell three-point functions to all orders in α′. a simple pattern emerges when comparing with the analogous bosonic and heterotic three-point functions. as in these theories, the amplitudes factorize. the theory has no gauss-bonnet term, but contains a riemann-cubed interaction to second order in α′.