HIDDEN SYMMETRIES IN DILATON GRAVITY

sigma-model representation is derived for the Einstein-Maxwell-dilaton system with an arbitrary dilaton coupling constant in four-dimensiona l space-time admitting a Killing vector held. Target space is shown to possess a five-parameter isometry group for an arbitrary value of the dilaton coupling constant alpha. For alpha = 0 it enlarges to a nine- parameter SU(2,1)xR generalizing the Kinnersley group of the Einstein- Maxwell theory. For alpha = root 3 hidden symmetry is realized by the eight-parameter group SL(3,R) corresponding to the vacuum five-dimensi onal Kaluza-Klein theory with two commuting Killing vectors. By direct computation of the target space Riemann tenser it is shown that, for any other value of alpha, target space is not a symmetric space. Howev er, static truncations of the model are found to possess a symmetric t arget space for an arbitrary value of the dilaton coupling constant. F inite four-parameter symmetry transformations are derived for dilaton electrostatics and magnetostatics and their subclass preserving an asy mptotic flatness is indicated. Electric and magnetic dilaton counterpa rts to static asymptotically hat vacuum solutions (Weyl class) are con structed.