No leftons for heterotic superstrings

We address the question whether the group-manifold reformulation of D=4 fermionic superstrings can be generalized through the use of the lefton-righton formalism. We show that in heterotic superstring models with world-sheet supersymmetry sitting in the left sector the cancellation of the Siegel anomaly forbids the presence of leftons and of non-moving bosons. Rightons are allowed and can replace some, but not all of the heterotic fermions. We also give the supersymmetric extension of the classical action for non-movers and we explain the origin of its peculiar structure within a first-order formulation. (orig.)