HETEROTIC STRING SOLUTIONS AND COSET CONFORMAL FIELD-THEORIES

We discuss solutions of the heterotic string theory which are analogou s to bosonic and superstring backgrounds related to coset conformal fi eld theories. A class of exact ''left-right symmetric'' solutions is o btained by supplementing the metric, antisymmetric tensor and dilaton of the superstring solutions by the gauge field background equal to th e generalised Lorentz connection with torsion. As in the superstring c ase, these backgrounds are alpha'-independent, i.e. have ''semiclassic al'' form. The corresponding heterotic string sigma model is obtained from the combination of the (1, 0) supersymmetric gauged WZNW action w ith the action of internal fermions coupled to the target space gauge field. The pure (1, 0) supersymmetric gauged WZNW theory is anomalous and does not describe a consistent heterotic string solution. We also find (to the order alpha'3 ) a two-dimensional perturbative heterotic string solution with the trivial gauge field background. To the leadin g order in alpha' it coincides with the known SL(2, R)/U(1) bosonic or superstring solutions. This solution does not correspond to a 'hetero tic' combination of the left superstring and right bosonic L0-operator s at the conformal field theory level. Some duality properties of the heterotic string solutions are studied.