Schubert classes in the equivariant cohomology of the Lagrangian Grassmannian

Takeshi Ikeda

Published 2005-08-05, updated 2006-05-11Version 3

Let $LG_n$ denote the Lagrangian Grassmannian parametrizing maximal isotropic (Lagrangian) subspaces of a fixed symplectic vector space of dimension $2n.$ For each strict partition $\lambda=(\lambda_1,...,\lambda_k)$ with $\lambda_1\leq n$ there is a Schubert variety $X(\lambda).$ Let $T$ denote a maximal torus of the symplectic group acting on $LG_n.$ Consider the $T$-equivariant cohomology of $LG_n$ and the $T$-equivariant fundamental class $\sigma(\lambda)$ of $X(\lambda).$ The main result of the present paper is an explicit formula for the restriction of the class $\sigma(\lambda)$ to any torus fixed point. The formula is written in terms of factorial analogue of the Schur $Q$-function, introduced by Ivanov. As a corollary to the restriction formula, we obtain an equivariant version of the Giambelli-type formula for $LG_n.$ As another consequence of the main result, we obtained a presentation of the ring $H_T^*(LG_n).$