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Crossing a unit slab of the symplectization costs a definite amount of energy

Proved
FiniteEnergyPlane.exists_pos_le_lintegral_energyDensity_annulus

by Mazecto · Oct 26, 2026 · Mathlib 0df444a (Lean v4.33.1)

finite-energypseudoholomorphic-curvessymplectic-geometry

Let S=H−1(1)⊂R2n+2S=H^{-1}(1)\subset\mathbb R^{2n+2}S=H−1(1)⊂R2n+2 be a strictly star-shaped level with contact form λ=λ0∣S\lambda=\lambda_0|_Sλ=λ0​∣S​ and dλd\lambdadλ-compatible complex structure JJJ on ξ\xiξ, and let u=(a,w):D˙=D∖{0}→R×S≅R2n+2∖{0}u=(a,w):\dot D=D\setminus\{0\}\to\mathbb R\times S\cong\mathbb R^{2n+2}\setminus\{0\}u=(a,w):D˙=D∖{0}→R×S≅R2n+2∖{0} be a finite-energy J~\tilde JJ~-holomorphic curve on the punctured unit disc. For a level A∈RA\in\mathbb RA∈R let φA(s)=χ(s−A)2\varphi_A(s)=\chi(s-A)^2φA​(s)=χ(s−A)2, where χ\chiχ is Mathlib's smooth transition function (χ=0\chi=0χ=0 on (−∞,0](-\infty,0](−∞,0], χ=1\chi=1χ=1 on [1,∞)[1,\infty)[1,∞)). Then there is a constant c>0c>0c>0 with the following property. For every level AAA and all radii 0<ρ2<ρ1<10<\rho_2<\rho_1<10<ρ2​<ρ1​<1 such that a∘u≤Aa\circ u\le Aa∘u≤A on one of the circles ∣z∣=ρi|z|=\rho_i∣z∣=ρi​ and a∘u≥A+1a\circ u\ge A+1a∘u≥A+1 on the other,

∫ρ2≤∣z∣<ρ1u∗d(φA(a)λ)  ≥  c.\int_{\rho_2\le|z|<\rho_1} u^*d(\varphi_A(a)\lambda)\;\ge\;c .∫ρ2​≤∣z∣<ρ1​​u∗d(φA​(a)λ)≥c.

In words: whenever uuu crosses a unit slab A≤a≤A+1A\le a\le A+1A≤a≤A+1 of the symplectization between two circles about the puncture, the Hofer-energy integrand at that level over the annulus is at least ccc, and ccc does not depend on the level AAA or on the radii. This is a step in the zero-charge case of the asymptotic description of finite-energy punctured discs (Hofer; Wendl, Theorem 9.8).

Formalization Note R×S\mathbb R\times SR×S is identified with R2n+2∖{0}\mathbb R^{2n+2}\setminus\{0\}R2n+2∖{0} by (a,x)↦e2ax(a,x)\mapsto e^{2a}x(a,x)↦e2ax, and aaa is aCoord H. The integrand of u∗d(φ(a)λ)u^*d(\varphi(a)\lambda)u∗d(φ(a)λ) with respect to ds∧dtds\wedge dtds∧dt is energyDensity H φ u; the integral is the lower Lebesgue integral of its positive part over ball 0 ρ₁ \ ball 0 ρ₂.

Preamble
import Definitions.Def_FiniteEnergyPlane_Setting
import Mathlib.Analysis.SpecialFunctions.SmoothTransition
Formal statement
namespace FiniteEnergyPlane

open MeasureTheory Metric Filter Topology
open scoped ContDiff ENNReal Real

/-- Crossing a unit slab costs a definite amount of energy, uniformly in the level. Let
`φ_A(s) = smoothTransition(s - A)²`. There is `c > 0` such that for every level `A` and all radii
`0 < ρ₂ < ρ₁ < 1` for which `a = aCoord ∘ u` is `≤ A` on one of the circles `‖z‖ = ρᵢ` and
`≥ A + 1` on the other, the energy density `u*d(φ_A(a) λ)` integrates to at least `c` over the
annulus `ρ₂ ≤ ‖z‖ < ρ₁`. -/
theorem exists_pos_le_lintegral_energyDensity_annulus {n : ℕ} (H : V n → ℝ)
    (hH : IsStrictlyStarShapedLevel H) (J : V n → V n →L[ℝ] V n)
    (hJ : IsCompatibleXiStructure H J) (u : ℂ → V n)
    (hu : IsFiniteEnergyCurve H J (ball 0 1 \ {0}) u) :
    ∃ c : ℝ, 0 < c ∧ ∀ A ρ₁ ρ₂ : ℝ, 0 < ρ₂ → ρ₂ < ρ₁ → ρ₁ < 1 →
      (((∀ z : ℂ, ‖z‖ = ρ₁ → aCoord H (u z) ≤ A) ∧
          ∀ z : ℂ, ‖z‖ = ρ₂ → A + 1 ≤ aCoord H (u z)) ∨
        ((∀ z : ℂ, ‖z‖ = ρ₁ → A + 1 ≤ aCoord H (u z)) ∧
          ∀ z : ℂ, ‖z‖ = ρ₂ → aCoord H (u z) ≤ A)) →
      ENNReal.ofReal c ≤ ∫⁻ z in ball 0 ρ₁ \ ball 0 ρ₂,
        ENNReal.ofReal (energyDensity H (fun s => Real.smoothTransition (s - A) ^ 2) u z) := by
  sorry

end FiniteEnergyPlane
Source
H. Hofer, Pseudoholomorphic curves in symplectizations with applications to the Weinstein conjecture in dimension three, Invent. Math. 114 (1993), 515-563, Section 3; C. Wendl, Lectures on Symplectic Field Theory, arXiv:1612.01009, Lemmas 9.14 and 9.17

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