HETEROTIC STRING SOLUTIONS AND COSET CONFORMAL FIELD-THEORIES

We discuss solutions of the heterotic string theory which are analogous to bosonic and superstring backgrounds related to coset conformal field theories. A class of exact ''left-right symmetric'' solutions is obtained by supplementing the metric, antisymmetric tensor and dilaton of the superstring solutions by the gauge field background equal to the generalised Lorentz connection with torsion. As in the superstring case, these backgrounds are alpha'-independent, i.e. have ''semiclassical'' form. The corresponding heterotic string sigma model is obtained from the combination of the (1, 0) supersymmetric gauged WZNW action with 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 leading order in alpha' it coincides with the known SL(2, R)/U(1) bosonic or superstring solutions. This solution does not correspond to a 'heterotic' combination of the left superstring and right bosonic L0-operators at the conformal field theory level. Some duality properties of the heterotic string solutions are studied.