Surface terms in the effective actions via duality constraints

Abstract: The effective action of string theory on a spacetime manifold with boundary has both bulk and boundary terms. We propose that both bulk and boundary actions, may be found by imposing the effective action to be invariant under the gauge transformations and under the string dualities. Using this proposal at the leading order of $\alpha'$, the standard Gibbons-Hawking-York boundary term is reproduced.