FIELD IDENTIFICATION FIXED-POINTS IN N=2 COSET THEORIES

We discuss N = 2 coset models with fixed points in their field identification. We determine the corrections to the modular transformations that are needed to resolve the fixed points, and show how to obtain the correct fusion rules. Furthermore we obtain the complete set of chiral Ramond ground states for the grassmannian coset models, and compute the resulting string spectra (number of generations N(g) and anti-generations N(a)) for diagonal invariants. A useful tool in these computations is the Poincare polynomial of the chiral ring, extended with an extra variable to characterize the intersection of the spinor current orbit and the chiral ring. For the non-grassmannian coset theories it is straightforward to compute the Poincare polynomial, but there is an additional technical complication in obtaining the extended polynomial. We show how to circumvent this problem and obtain N(g) and N(a) also for tensor products of these cosets.