T-duality constraints on higher derivatives revisited

We ask to what extent are the higher-derivative corrections of string theory constrained by T-duality. The seminal early work by Meissner tests T-duality by reduction to one dimension using a distinguished choice of field variables in which the bosonic string action takes a Gauss-Bonnet-type form. By analyzing all field redefinitions that may or may not be duality covariant and may or may not be gauge covariant we extend the procedure to test T-duality starting from an action expressed in arbitrary field variables. We illustrate the method by showing that it determines uniquely the first-order α′ corrections of the bosonic string, up to terms that vanish in one dimension. We also use the method to glean information about the O(α²) corrections in the double field theory with Green-Schwarz deformation.