  We investigate a modification of the 2+1 dimensional abelian Chern-Simons
theory, obtained by adding a Proca mass term to the gauge field. We are
particularly interested in the infrared limit, which can be described by two
{\it a priori} different "topological" quantum mechanical models. We apply
methods of equivariant cohomology and the ensuing supersymmetry to analyze the
partition functions of these quantum mechanical models. In particular, we find
that a previously discussed phase-space reductive limiting procedure which
relates these two models can be seen as a direct consequence of our
supersymmetry.
