Semi-global invariants of piecewise smooth Lagrangian fibrations

Abstract

We study certain types of piecewise smooth Lagrangian fibrations of smooth symplectic manifolds, which we call stitched Lagrangian fibrations. We extend the classical theory of action-angle coordinates to these fibrations by encoding the information on the non-smoothness into certain invariants consisting, roughly, of a sequence of closed 1-forms on a torus. The main motivation for this work is given by the piecewise smooth Lagrangian fibrations previously constructed by the authors (in Some piece-wise smooth Lagrangian fibrations, http://seminariomatematico.dm.unito.it/rendiconti/63-3.html), which topologically coincide with the local models used by M. Gross in his paper "Topological Mirror Symmetry", http://arxiv.org/abs/math.AG/9909015..