Symplectization of certain Hamiltonian systems in fibered almost-symplectic manifolds

TL;DR

This paper explores the properties of Hamiltonian vector fields in almost-symplectic manifolds with Lagrangian torus fibrations, revealing conditions under which they resemble standard symplectic Hamiltonian fields.

Contribution

It introduces the concept of partially-Hamiltonian and fully-Hamiltonian vector fields in almost-symplectic manifolds and analyzes their existence and behavior under certain conditions.

Findings

Non-vertical fully-Hamiltonian vector fields exist.

Under generic conditions, these fields reduce to standard symplectic-Hamiltonian vector fields.

The study extends Hamiltonian theory to almost-symplectic fibered manifolds.

Abstract

There is an important difference between Hamiltonian-like vector fields in an almost-symplectic manifold $(M,\sigma)$, compared to the standard case of a symplectic manifold: in the almost-symplectic case, a vector field such that the contraction iX{\sigma} is closed need not be a symmetry of $\sigma$. We thus call partially-Hamiltonian those vector fields which have the former property and fully-Hamiltonian those which have both properties. We consider 2n-dimensional almost symplectic manifolds with a fibration $\pi : M \longrightarrow B$ by Lagrangian tori. Trivially, all vertical partially-Hamiltonian vector fields are fully-Hamiltonian. We investigate the existence and the properties of non-vertical fully-Hamiltonian vector fields. We show that this class is non-empty, but under certain genericity conditions that involve the Fourier spectrum of their Hamiltonian, these vector fields reduce, under a (possibly only semi-globally defined, if $n \ge 4$) torus action, to families of standard symplectic-Hamiltonian vector fields.