Toric structures on near-symplectic 4-manifolds

David T. Gay ; Margaret Symington

Journal of the European Mathematical Society, Tome 11 (2009) no. 3, pp. 487-520

Résumé

A near-symplectic structure on a 4-manifold is a closed 2-form that is symplectic away from the 1-dimensional submanifold along which it vanishes and that satisfies a certain transversality condition along this vanishing locus. We investigate near-symplectic 4-manifolds equipped with singular Lagrangian torus fibrations which are locally induced by effective Hamiltonian torus actions. We show how such a structure is completely characterized by a singular integral affine structure on the base of the fibration whenever the vanishing locus is nonempty. The base equipped with this geometric structure generalizes the moment map image of a toric 4-manifold in the spirit of earlier work by the second author on almost toric symplectic 4-manifolds. We use the geometric structure on the base to investigate the problem of making given smooth torus actions on 4-manifolds symplectic or Hamiltonian with respect to near-symplectic structures and to give interesting constructions of structures which are locally given by torus actions but have nontrivial global monodromy.

Détail

DOI : 10.4171/jems/157

Classification : 57-XX, 00-XX
Keywords: Symplectic, near-symplectic, toric, torus action, four-manifold, Hamiltonian, Lagrangian fibration