Some features of (0, 2) moduli space

We discuss some aspects of perturbative (0, 2) Calabi-You moduli space. In particular, we show how models with different (0, 2) data can meet along various sub-loci in their moduli space. In the simplest examples, the models differ by the choice of desingularization of a holomorphic V-bundle over the same resolved Calabi-You base while in more complicated examples, even the smooth Calabi-You base manifolds can be topologically distinct. These latter examples extend and clarify a previous observation which was limited to singular Calabi-You spaces and seem to indicate a multicritical structure in moduli space. This should have a natural F-theory counterpart in terms of the moduli space of Calabi-You four-folds.