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Physics theoremStatement: AI-adaptedProof: AI-generatedPipeline-generatedprecheck passverified 2026-10-22 (gpt-6.1-sol)
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Paraxial orbital winding in its exact scalar domain

Physical scope

Conditional identity for a smooth, finite-transverse-norm scalar paraxial field in the specified angular-spectrum model, at a fixed propagation plane. The dimensionless scalar rotation generator is not identified with torque, total electromagnetic angular momentum, a photon angular momentum, or a general exact-vector spin/orbital decomposition. No empirical claim is made.

Statement

Fix a propagation plane z and let uz∈C∞(R2;C)∩L2(R2;C) be a scalar field in the paraxial model. Assume uz is nonzero as an L2 equivalence class. For r>0 write uz(rcos⁡ϕ,rsin⁡ϕ)=f(r)eiℓϕ, where ℓ∈Z and ϕ is read modulo 2π. Require a smooth axis extension; explicitly, assume there are ϵ>0 and a smooth complex-valued g:(−ϵ,ϵ)→C such that f(r)=r∣ℓ∣g(r2) for 0<r<ϵ. Define Lzsc:=−i(−y∂x+x∂y) and use the first-variable-linear L2 pairing ⟨v,w⟩2:=∫R2v(x,y)w(x,y)‾ d2x. Then the normalized scalar angular-generator expectation is ⟨Lzscuz,uz⟩2⟨uz,uz⟩2=ℓ.

Facts & Assumptions

Given: A fixed plane z, the stated smooth L2 scalar field uz with nonzero L2 class and the stated integer-winding form.

[F1]

The paraxial scalar field and its SI field interpretation are those of the angular-spectrum Definition. Forward angular-spectrum beam Framework-local SI units, the vacuum constants and the exact/measured status of their values

[F2]

The real partial derivatives are those on the fixed laboratory spatial slice, and complex exponentiation satisfies exp⁡′=exp⁡. Directional derivatives and partial derivatives of a map U⊆Rm→Rn The complex exponential is entire and its complex derivative is itself

[F3]

The field uses the complex exponential and conjugation/modulus operations defined on all complex numbers. The complex exponential by its power series Real and imaginary parts, complex conjugation, and modulus

[F4]

On each local polar-coordinate chart with r>0, the smooth map (r,ϕ)↦(x,y)=(rcos⁡ϕ,rsin⁡ϕ) has ∂ϕx=−y and ∂ϕy=x. The chain rule therefore gives ∂ϕuz=−y∂xuz+x∂yuz there. The chain rule for total derivatives: D(g∘f)(a)=Dg(f(a))∘Df(a)

Proof

1.1givenF1F2F3F4algebra

For r>0, [F4] identifies the angular vector field −y∂x+x∂y with ∂ϕ. By [F2]–[F3], differentiating the integer winding factor gives Lzscuz=−i∂ϕ(feiℓϕ)=ℓfeiℓϕ=ℓuz. The required axis form makes uz smooth at the origin: for ℓ≥0 its angular factor is (x+iy)ℓ, and for ℓ<0 it is (x−iy)∣ℓ∣, each multiplied by the smooth radial factor g(x2+y2). The rotation vector field vanishes at the origin, so the same identity holds there as well.

2.1step 1.1givenalgebra∎

Step 1.1 gives Lzscuz=ℓuz everywhere, hence Lzscuz∈L2 because uz∈L2(R2;C). Therefore ⟨Lzscuz,uz⟩2=∫R2ℓ∣uz∣2 d2x=ℓ⟨uz,uz⟩2; the denominator is positive since uz is nonzero. Division proves the claimed identity.

Remarks

The axis hypothesis is stated as a smooth extension condition; the bound f(r)=O(r∣ℓ∣) alone would not guarantee smoothness. No radial integration by parts is used. The scalar generator is dimensionless and does not by itself determine a torque or a photon angular momentum.

Depends on

Dependency tree · 2 levels

Sources