Matthias Franz
Koszul duality for tori

2001, 100 Seiten, € 65,45. ISBN 3-89649-748-0

Koszul duality refers (in its simplest form) to the equivalence of derived categories of differential modules over symmetric and exterior algebras. Goresky, Kottwitz, and MacPherson have shown that one can use Koszul duality to compute the real equivariant cohomology of a G-space as H*(BG)-module from the non-equivariant cochain complex. Similarly, the equivariant cochain complex determines the ordinary cohomology as H*(G)-module.
We present, for the case of torus actions and singular cohomology, a new proof which extends to arbitrary coefficients. It permits moreover to recover the product structures in cohomology. As an application, we determine the integral cohomology of smooth toric varieties, thereby refining a result of Buchstaber and Panov.

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