Hard Lefschetz theorem and Hodge-Riemann relations for intersection cohomology of nonrational polytopes

P. Bressler, V. A. Lunts

Published 2003-02-19, updated 2003-09-17Version 3

The Hard Lefschetz theorem for intersection cohomology of nonrational polytopes was recently proved by K. Karu [Ka]. This theorem implies the conjecture of R. Stanley on the unimodularity of the generalized $h$-vector. In this paper we strengthen Karu's theorem by introducing a canonical bilinear form $(\cdot ,\cdot)_{\Phi}$ on the intersection cohomology $IH(\Phi)$ of a complete fan $\Phi$ and proving the Hodge-Riemann bilinear relations for $(\cdot ,\cdot)_{\Phi}$.