Star-shaped approximations of a Hamiltonian, agreeing with it to first order along two periodic orbits, for which these orbits and all their iterates are non-degenerate
OpenHryniewiczCriterion.exists_approx_nondegenerate_along_orbitsdynamical-systemsgeometry-topologysymplectic-geometry
Let be a strictly star-shaped level and let , be periodic orbits of on . Then there is a sequence of Hamiltonians such that
- every level is strictly star-shaped;
- every periodic orbit of on whose image lies in (that is, , and all their iterates, with any time shift) is non-degenerate;
- and at every point of ;
- in .
in means: for every and every compact , uniformly on . A periodic orbit on (prime or not) is non-degenerate when, for its linearized flow , the linearized return map on , written in the global frame as the matrix of linearizedXiPath, does not have as an eigenvalue. A Hamiltonian is non-degenerate when all its periodic orbits on the level are.
By (3), along both orbits, so and stay periodic orbits of every . Nothing is asserted about the other periodic orbits of . In contact language: carries with in , and on the two orbits, and the two orbits are non-degenerate for .
Preamble
import Definitions.Def_HryniewiczCriterion_ConleyZehnder import Definitions.Def_HryniewiczCriterion_GlobalSection import Definitions.Def_HryniewiczCriterion_SelfLinking open HryniewiczCriterion
Formal statement
theorem HryniewiczCriterion.exists_approx_nondegenerate_along_orbits (H : R4 → ℝ) (hS : IsStrictlyStarShapedLevel H) (P Q : PeriodicOrbit H) :
∃ Hs : ℕ → R4 → ℝ, (∀ k, IsStrictlyStarShapedLevel (Hs k)) ∧
(∀ k (R : PeriodicOrbit (Hs k)), R.image ⊆ P.image ∪ Q.image →
∀ (Y : ℝ → (R4 →L[ℝ] R4)), IsLinearizedFlow (Hs k) R.x Y →
∀ v : Fin 2 → ℝ, (linearizedXiPath (Hs k) R Y 1).mulVec v = v → v = 0) ∧
(∀ k, ∀ y ∈ P.image ∪ Q.image, Hs k y = H y ∧ fderiv ℝ (Hs k) y = fderiv ℝ H y) ∧
(∀ m : ℕ, ∀ K : Set R4, IsCompact K →
TendstoUniformlyOn (fun k => iteratedFDeriv ℝ m (Hs k)) (iteratedFDeriv ℝ m H) Filter.atTop K) := by sorry
Source
U. Hryniewicz, Systems of global surfaces of section for dynamically convex Reeb flows on the 3-sphere, J. Symplectic Geom. 12 (2014) 791-862, arXiv:1105.2077, Section 3.3, proof of Lemma 3.12 (p. 26: the sequence ), and (28)-(29) on p. 20.