Geometric properties and flux of locally conformally symplectic diffeomorphisms

TL;DR

This paper explores the geometric, topological, and dynamical properties of locally conformally symplectic (LCS) diffeomorphisms, extending fundamental symplectic results and introducing invariants that account for conformal structures.

Contribution

It develops LCS analogues of key symplectic theorems, characterizes Hamiltonian subgroups via flux, and introduces a Twisted Calabi invariant for non-exact LCS structures.

Findings

Established a short exact sequence for the Hamiltonian subgroup in LCS setting.

Developed an LCS version of the Weinstein neighborhood theorem.

Introduced a Twisted Calabi invariant for non-exact LCS structures.

Abstract

We investigate the geometric and topological properties of the group of locally conformally symplectic (LCS) diffeomorphisms, utilizing the LCS flux homomorphism defined by S. Haller. By analyzing the flux map from the universal cover of the identity component $(\ker \Phi)_0$ to the first Lichnerowicz cohomology group $H_\omega^1(M)$, we establish a short exact sequence characterizing the Hamiltonian subgroup $\Ham_\Omega(M)$ and provide conditions for its topological splitting as a semidirect product. We develop LCS analogues of fundamental symplectic results, including a Weinstein neighborhood theorem, a flux rigidity theorem for homotopies, and a characterization of LCS structures on mapping tori. A central theme of this work is the influence of the Hodge decomposition of the Lee form $\omega = dh + l$. In the exact case ($l=0$), we utilize the global conformal equivalence to symplectic structures to establish energy-capacity inequalities, an LCS Hofer metric, and non-displaceability results. We explicitly analyze the relationship between the LCS Calabi invariant and its symplectic counterpart, showing they are controlled by a multiplicative factor depending on the conformal weight. For the general non-exact case ($l \neq 0$), we introduce a Twisted Calabi invariant that captures the interaction between Hamiltonian dynamics and the harmonic component of the Lee form.