  The article is devoted to a quantum field theory explanation of the
relationship (noticed some years ago by Gepner) between the Verlinde algebra of
the group $U(k)$ at level $N-k$ and the cohomology of the Grassmannian. The
argument proceeds by starting with the two dimensional sigma model whose target
space is the Grassmannian and integrating out some fields in a standard way. It
has long been known that the resulting low energy effective action describes a
theory with a mass gap; the novelty here is that this theory in fact is
equivalent at long distances to a gauged WZW model of $U(k)/U(k)$, and hence is
related to the Verlinde algebra.
