Solitons of axion-dilaton gravity

We use soliton techniques of the two-dimensional reduced beta-function equations to obtain nontrivial string backgrounds from flat space. These solutions are characterized by two integers (n,m) referring to the soliton numbers of the metric and axion-dilaton sectors, respectively. We show that the Nappi-Witten universe associated with the SL(2) X SU(2)SO(1,1) X U(1) CFT coset arises as a (1,1) soliton in this fashion for certain values of the moduli parameters, while for other values of the soliton moduli we arrive at the SL(2)/SO(1,1) X SO(1,1)(2) background. Ordinary four-dimensional black holes arise as two-dimensional (2,0) solitons, while the Euclidean wormhole background is described as a (0,2) soliton on flat space. The soliton transformations correspond to specific elements of the string Geroch group. These could be used as a starting point for exploring the role of U dualities in string compactifications to two dimensions.