EXACTLY SOLVABLE POINTS IN THE MODULI SPACE OF HETEROTIC N=2 STRINGS

We investigate the subset of exactly solvable (0, 4) worldsheet supersymmetric string vacua contained in a recent class of Gepner-like (0, 2) superconformal models. The identification of these models with certain points of enhanced gauge symmetry on K3×T2 can be achieved completely. Furthermore, we extend the construction of in general (0, 2) supersymmetric exactly solvable models to the case where also a nontrivial part of the vector bundle is embedded into the hidden E8 gauge group. For some examples we explicitly calculate the enhanced gauge symmetries and show that they open up the way to interesting branches of the N=2 moduli space. For some of these models candidates of type-II dual descriptions exist.