Abstract
Let $H\to \mathbb{R}^4\to \mathbb{R}$ be any smooth function. This article introduces some arguments for extracting dynamical information about the Hamiltonian flow of $H$ from high-dimensional families of closed holomorphic curves. We work in a very general setting, without imposing convexity or contact-type assumptions.
For any compact regular level set $Y$, we prove that the Hamiltonian flow admits an finite family of pairwise distinct, proper, compact invariant subsets whose union is dense in $Y$. This is a generalization of the Fish–Hofer theorem, which shows that $Y$ has at least one proper compact invariant subset. We then establish a global Le Calvez–Yoccoz property for almost every compact regular level set $Y$: any compact invariant subset containing all closed orbits is either equal to $Y$ or is not locally maximal. Next, we prove quantitative versions, in four dimensions, of the celebrated almost-existence theorem for Hamiltonian systems; such questions have been open for general Hamiltonians since the late 1980s. We prove that almost every compact regular level set of $H$ contains at least two closed orbits, a sharp lower bound. Under explicit and $C^\infty$-generic conditions on $H$, we prove almost-existence of infinitely many closed orbits.
