Charging Symmetries and Linearizing Potentials for Heterotic String in Three Dimensions

Using the Ernst potential formulation we construct all it finite symmetry transformations which preserve asymptotics of the bosonic fields of the (d+3)--dimensional low--energy heterotic string theory compactified on a d--torus. We combine all the dynamical variables into a single (d+1)X(d+1+n)--dimensional matrix potential which linearly transforms under the action of these symmetry transformations in a transparent SO(2,d-1) X SO(2,d-1+n) way, where n is the number of Abelian vector fields. We formulate the most general solution generation technique based on the use of these symmetries and show that they form an invariance group of the general Israel--Wilson--Perj'es class of solutions.