beta Symmetry of Supergravity

Continuous O(d, d) global symmetries emerge in Kaluza-Klein reductions of D-dimensional string supergravities to D - d dimensions. We show that the nongeometric elements of this group effectively act in the D-dimensional parent theory as a hidden bosonic symmetry that fixes its couplings: the /3 symmetry. We give the explicit /3 transformations to first order in alpha' and verify the invariance of the action as well as the closure of the transformation rules.