Supersymmetry and dualities

Duality transformations with respect to rotational isometrics relate supersymmetric with non-supersymmetric backgrounds in string theory. We find that non-local world-sheet effects have to be taken into account in order to restore supersymmetry at the string level. The underlying superconformal algebra remains the same, but in this case T-duality relates local with non-local realisations of the algebra in terms of parafermions. This is another example where stringy effects resolve paradoxes of the effective field theory. (orig.)