English

On the Hofer geometry injectivity radius conjecture

Symplectic Geometry 2016-02-09 v3 Differential Geometry

Abstract

We verify here some variants of topological and dynamical flavor of the injectivity radius conjecture in Hofer geometry, Lalonde-Savelyev \cite{citeLalondeSavelyevOntheinjectivityradiusinHofergeometry} in the case of Ham(S2)Ham (S^2) and Ham(Σ,ω)Ham(\Sigma, \omega), for Σ\Sigma a closed positive genus surface. In particular we show that any loop in Ham(S2)Ham (S^2), respectively Ham(Σ,ω)Ham(\Sigma, \omega) with L+L ^{+} Hofer length less than area(S2)/2area(S ^{2} )/2, respectively any L+L ^{+} length is contractible through (L+L ^{+} ) Hofer shorter loops, in the CC ^{\infty} topology. We also prove some stronger variants of this statement on the loop space level. One dynamical type corollary is that there are no smooth, positive Morse index (Ustilovsky) geodesics, in Ham(S2)Ham (S^2), respectively in Ham(Σ,ω)Ham(\Sigma, \omega) with L+L ^{+} Hofer length less than area(S2)/2area (S ^{2} )/2, respectively any length. The above condition on the geodesics can be expanded as an explicit and elementary dynamical condition on the associated Hamiltonian flow. We also give some speculations on connections of this later result with curvature properties of the Hamiltonian diffeomorphism group of surfaces.

Keywords

Cite

@article{arxiv.1501.02740,
  title  = {On the Hofer geometry injectivity radius conjecture},
  author = {Yasha Savelyev},
  journal= {arXiv preprint arXiv:1501.02740},
  year   = {2016}
}

Comments

This version to appear in Int. Math. Res. Not. Somewhat major revision, the $L^{\infty}$ version of the main result had to be removed, and requires more work. Many changes to notation and structure

R2 v1 2026-06-22T07:58:42.992Z