Cohomology of GKM-sheaves

Abstract

Let $T$ be a compact torus and $X$ be a a finite $T$-CW complex (e.g. a compact $T$-manifold). In earlier work, the second author introduced a functor which assigns to $X$ a so called GKM-sheaf ${\mathcal{F}}_X$ whose ring of global sections $H^0({\mathcal{F}}_X)$ is isomorphic to the equivariant cohomology $H_T^{\ast }(X)$ whenever $X$ is equivariantly formal (meaning that $H_T^{\ast }(X)$ is a free module over $H^{\ast }(BT))$. In the current paper we prove more generally that $H^0({\mathcal{F}}_X)\cong H_T^{\ast }(X)$ if and only if $H_T^{\ast }(X)$ is reflexive, and find a geometric interpretation of the higher cohomology $H^n({\mathcal{F}}_X)$ for $n\ge 1$.

13 pages