Infinitely many non-isotopic real symplectic forms on $S^2\times S^2$

Abstract

Let $(S^2,\omega )$ be a symplectic sphere, and let $\tau :S^2\to S^2$ be an anti-symplectic involution of $(S^2,\omega )$. We consider the product $(S^2,\omega )\times (S^2,\omega )$ endowed with the anti-symplectic involution $\tau \times \tau$, and study the space of monotone anti-invariant symplectic forms on this four-manifold. We show that this space is disconnected. In addition, during the course of the proof, we produce a diffeomorphism of the grassmannian (2,4) which induces the identity map on all homology and homotopy groups, but which is not homotopic to the identity.

9 pages; nothing's changed; accepted for publication by the Journal of Topology