Generalized geometry, equivariant $\bar{\partial}\partial$-lemma, and torus actions

Yi Lin

Published 2006-07-18, updated 2007-03-11Version 2

In this paper we first consider the Hamiltonian action of a compact connected Lie group on an $H$-twisted generalized complex manifold $M$. Given such an action, we define generalized equivariant cohomology and generalized equivariant Dolbeault cohomology. If the generalized complex manifold $M$ satisfies the $\bar{\partial}\partial$-lemma, we prove that they are both canonically isomorphic to $(S\g^*)^G\otimes H_H(M)$, where $(S\g^*)^G$ is the space of invariant polynomials over the Lie algebra $\g$ of $G$, and $H_H(M)$ is the $H$-twisted cohomology of $M$. Furthermore, we establish an equivariant version of the $\bar{\partial}\partial$-lemma, namely $\bar{\partial}_G\partial$-lemma, which is a direct generalization of the $d_G\delta$-lemma for Hamiltonian symplectic manifolds with the Hard Lefschetz property. Second we consider the torus action on a compact generalized K\"ahler manifold which preserves the generalized K\"ahler structure and which is equivariantly formal. We prove a generalization of a result of Carrell and Lieberman in generalized K\"ahler geometry. We then use it to compute the generalized Hodge numbers for non-trivial examples of generalized K\"ahler structures on $\C\P^n$ and $\CP^n$ blown up at a fixed point.