Bi-invariant metrics on the group of symplectomorphisms

Abstract

This paper studies the extension of the Hofer metric and general Finsler metrics on Hamiltonian symplectomorphism group $Ham(M,ω)$ to the identity component $Symp_0(M,ω)$ of symplectomorphism group. In particular, we prove that the Hofer metric on $Ham(M,ω)$ does not extend to a bi-invariant metric on $Symp_0(M,ω)$ for many symplectic manifolds. We also show that for the torus $T^{2n}$ with the standard symplectic form $ω$, no Finsler metric on $Ham(T^{2n},ω)$ that satisfies a strong form of the invariance condition can extend to a bi-invariant metric on $Symp_0(T^{2n},ω)$. Another interesting result is that there exists no $C^1$-continuous bi-invariant metric on $Symp_0(T^{2n},ω)$.