Symplectization of certain Hamiltonian systems in fibered almost-symplectic manifolds

There is an important difference between Hamiltonian-like vector fields in an almost-symplectic manifold (M,σ), compared to the standard case of a symplectic manifold: in the almost-symplectic case, a vector field such that the contraction iXσ is closed need not be a symmetry of σ. 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 π:M→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≥4) torus action, to families of standard symplectic-Hamiltonian vector fields.