Integrable systems on singular symplectic manifolds: From local to global

TL;DR

This paper explores integrable systems on singular symplectic manifolds with order one degeneracies, establishing an action-angle theorem for folded cases and analyzing topological obstructions to global coordinates.

Contribution

It introduces a new action-angle theorem for folded symplectic integrable systems and investigates topological obstructions affecting global coordinate existence.

Findings

Proved an action-angle theorem for folded symplectic integrable systems.

Identified topological obstructions related to the critical set topology.

Showed that global action-angle coordinates may not exist due to these obstructions.

Abstract

In this article we consider integrable systems on manifolds endowed with singular symplectic structures of order one. These structures are symplectic away from an hypersurface where the symplectic volume goes either to infinity or to zero in a transversal way (singularity of order one) resulting either in a $b$-symplectic form or a folded symplectic form. The hypersurface where the form degenerates is called critical set. We give a new impulse to the investigation of the existence of action-angle coordinates for these structures initiated in [KM] and [KMS] by proving an action-angle theorem for folded symplectic integrable systems. Contrary to expectations, the action-angle coordinate theorem for folded symplectic manifolds cannot be presented as a cotangent lift as done for symplectic and $b$-symplectic forms in [KM]. Global constructions of integrable systems are provided and obstructions for global existence of action-angle coordinates are investigated in both scenarios. The new topological obstructions found emanate from the topology of the critical set $Z$ of the singular symplectic manifold. The existence of these obstructions in turn implies the existence of singularities for the integrable system on $Z$.