The cohomology rings of abelian symplectic quotients
  Let $M$ be a symplectic manifold, equipped with a Hamiltonian action of a torus $T$. We give an explicit formula for the rational cohomology ring of the symplectic quotient $M//T$ in terms of the cohomology ring of $M$ and fixed point data. Under some restrictions, our formulas apply to integral cohomology. In certain cases these methods enable us to show that the cohomology of the reduced space is torsion-free. 
Susan Tolman (University of Illinois at Urbana-Champaign), Jonathan   Weitsman (University of California, Santa Cruz)