Mathematical Research Letters

Volume 13, Issue 6, November 2006 pp. 985-999.

The Maslov index as a quadratic space

Authors: Teruji Thomas
Author institution: Merton College, Oxford University

Summary: Kashiwara defined the Maslov index (associated to a collection of Lagrangian subspaces of a symplectic vector space over a field $F$) as a class in the Witt group $W(F)$ of quadratic forms. We construct a canonical quadratic vector space in this class and show how to understand the basic properties of the Maslov index without passing to $W(F)$---that is, more or less, how to upgrade Kashiwara's equalities in $W(F)$ to canonical isomorphisms between quadratic spaces. The quadratic space is defined using elementary linear algebra. On the other hand, it has a nice interpretation in terms of sheaf cohomology, due to A. Beilinson.

Contents Full-Text PDF