Inverting the Hamiltonian Reduction in String Theory

Abstract

It is well known that many interesting realisations of string theories can be obtained via hamiltonian reduction from WZW models. I want to point out that string theories do in certain cases also provide the recipe to reconstruct the ambient space of the hamiltonian reduction, including Kac--Moody currents and the associated ghosts. The procedure of reconstructing the Kac--Moody currents is closely related to properties of matter+gravity multiplets in noncritical string theories. In application to KPZ gravity and its N=1 supersymmetric extension, the `inverted hamiltonian reduction' constructions serve to establish relation with the DDK-type formalism for matter + gravity.