The bounded isometry conjecture for symplectomorphism groups

Let (M,ω)(M,\omega) be a closed symplectic manifold with symplectic form ω\omega. Let Ham(M,ω)\operatorname{Ham}(M,\omega) be its Hamiltonian group and let Symp0(M,ω)\operatorname{Symp}_0(M,\omega) be the identity component of its symplectomorphism group. For ϕSymp(M,ω)\phi\in\operatorname{Symp}(M,\omega), define

r(ϕ):=sup{ρ([ϕ,f])fHam(M,ω)},r(\phi):=\sup\{\rho([\phi,f])\mid f\in\operatorname{Ham}(M,\omega)\},

where ρ\rho is the Hofer norm on Ham(M,ω)\operatorname{Ham}(M,\omega) and [ϕ,f]:=ϕfϕ1f1[\phi,f]:=\phi f\phi^{-1}f^{-1}. A symplectomorphism is bounded if r(ϕ)<r(\phi)<\infty, and let BI0(M,ω)\operatorname{BI}_0(M,\omega) denote the set of bounded elements of Symp0(M,ω)\operatorname{Symp}_0(M,\omega).

Bounded isometry conjecture. For all (M,ω)(M,\omega),

BI0(M,ω)=Ham(M,ω).\operatorname{BI}_0(M,\omega)=\operatorname{Ham}(M,\omega).

The conjecture asserts that every bounded symplectomorphism in the identity component is Hamiltonian. It would imply that every non-Hamiltonian element is unbounded, providing an obstruction to extending the Hofer metric to a bi-invariant metric on the full identity component.

Sources & referencesView supporting material

Primary source

Zhigang Han, “Bi-invariant metrics on the group of symplectomorphisms”, arXiv:math/0510569 (2005).

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