Abstract. We show that the dω-cohomology is isomorphic to a conformally invariant usual de Rham cohomology of an appropriate cover. We also prove a Moser theorem for locally conformal symplectic (lcs) forms. We point out a connection between lcs geometry and contact geometry. Finally, we show the connections between first kind, second kind, essential, inessential, local, and global conformal symplectic structures through several invariants.
Mathematics Subject Classification (2000). 53C12; 53C15.Keywords. Locally conformal symplectic structures, Lee form, extended Lee homomorphism, de Rham invariant, Gelfand-Fucks invariant, Lee invariant, conformal invariants, essential/inessential conformal structures, the dω cohomology, the cA-cohomology.
PreliminariesA locally conformal symplectic (lcs) form on a smooth manifold M is a nondegenerate 2-form Ω such that there exists an open cover U = (U i ) and smooth positive functions λ i on U i such thatis a symplectic form on U i . If for all i, λ i = 1, the form Ω is a symplectic form. Lee [15] observed that the 1-forms {d(ln λ i )} fit together into a closed 1-form ω such that dΩ = −ω ∧ Ω. Two lcs forms Ω, Ω on a smooth manifold M are said to be (conformally) equivalent if Ω = f Ω, for some positive function f on M .A locally conformal symplectic (lcs) structure S on a smooth manifold M is an equivalence class of lcs forms.