Journal of Symplectic Geometry

Volume 3 (2005)

Number 4

Moment maps, symplectomorphism groups and compatible complex structures

Pages: 655 – 670



Miguel Abreu Abreu

Gustavo Granja

Nitu Kitchloo


In this paper, we apply Donaldson's general moment map framework for the action of a symplectomorphism group on the corresponding space of compatible (almost) complex structures to the case of rational ruled surfaces. This gives a new approach to understanding the topology of their symplectomorphism groups, based on a result of independent interest: the space of compatible integrable complex structures on any symplectic rational ruled surface is (weakly) contractible. We also explain how in general, under this condition, there is a direct relationship between the topology of a symplectomorphism group, the deformation theory of compatible complex structures and the groups of complex automorphisms of these complex structures.

Published 1 January 2005