DILATON, MODULI AND STRING 5-BRANE DUALITY AS SEEN FROM 4 DIMENSIONS

A naive dimensional reduction of the N=1, D=10 supergravity theory that naturally arises in five-brane models is used to determine the role of two fields which are basic ingredients of string models: the dilaton and, among the moduli, the breathing mode. It is shown that, under the duality transformation that relates five-branes and strings, these two fields exchange the roles of the 10-dimensional dilaton and the radius of the compact manifold. A description of this phenomenon in terms of the linear multiplets of the 4-dimensional supergravity is also presented.