GENERALIZED STRING FUNCTIONS OF N=1 SPACE-TIME SUPERSYMMETRIC STRING VACUA

We present a dual formulation of the construction of N = 2 nonlinear sigma-model type conformal field theories with c = 9 which are mainly used as internal sectors of Calabi-Yau heterotic string compactifications. The supercurrents G(+/-)(z) and the higher components of the spectral flow superfields X(+/-)(z) + theta(+/-)Y(+/-)(z) turn out in each case to be tenser products of two simple currents of a c = 1 and a non-supersymmetric parafermionic c = 8 CFT. The characters of the latter model can be regarded as string functions of the coset sigma/U(1). In particular, for the (1)(9) Gepner model we discuss these string functions in detail, realizing this model contains a broken E(8) gauge symmetry of which only the abelian subalgebra remains a symmetry of the spectrum. As an example, we construct a simple model leading to a string theory with a massless spectrum of 36 E(6) generations and an extended gauge symmetry E(6) X SU(3)(4)