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Physics theoremStatement: AI-adaptedProof: AI-generatedPipeline-generatedprecheck passverified 2026-10-22 (gpt-6.1-sol)
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SO(2) helicity character and geometric phase

Physical scope

Conditional classical Maxwell-Lorentz vacuum model in the smooth source-free nonzero-Fourier-mode regime stated by the supplier, with no extra approximation. Rotations are proper active spatial rotations and parallel transport is that of the direction-sphere connection. This is the SO(2) helicity character, not a spin/orbital angular-momentum decomposition or a photon position operator; no dynamical time evolution, measured phase, material medium, quantization, or empirical claim is asserted.

Statement

For u,v∈C3, the dot and cross products are the complex-bilinear extensions with coordinate formulas u⋅v=∑j=13ujvj and u×v=(u2v3−u3v2,u3v1−u1v3,u1v2−u2v1), as defined in the helicity line-bundle item.

Fix n∈S2 and σ∈{+1,−1}. Put U(1):={z∈C:∣z∣=1}. For n∈R3 and z∈C3, the dot in the rotation formula is n⋅z=∑j=13njzj, the complex-bilinear dot product defined in the earlier helicity line-bundle definition. For the dimensionless angle α∈R/(2πZ), define the proper active rotation fixing n by Rn,αz=(n⋅z)n+cos⁡α (z−(n⋅z)n)+sin⁡α (n×z) on C3, with the complex-linear extension of the real rotation action, and set SO(2)n:={Rn,α:α∈R/(2πZ)}. It acts on the whole helicity fibre Lσ(n) by Rn,αz=e−iσαz, so the fibre carries the character ρσ(Rn,α)=e−iσα. For a piecewise C1 closed direction path γ:[0,1]→S2, choose a finite subdivision 0=t0<⋯<tm=1 on whose closed subintervals γ is C1. For each segment choose an open set Uj⊆S2 containing its image and a unit frame vj:Uj→C3 as defined in the helicity line-bundle definition; write Aj:=i∑ℓ=13(vj)ℓ‾ d(vj)ℓ. For a one-form Aj on Uj, define its oriented curve integral on this segment by ∫γ∣[tj−1,tj]Aj:=∫tj−1tj(Aj)γ(t)(γ˙(t)) dt, the ordinary Riemann integral of the continuous integrand on that segment. For a C1 section s(t)∈Lσ(γ(t)), define its projected derivative by ∇γ˙s(t):=Pσ(γ(t))s˙(t), with the derivative taken componentwise in C3; parallel transport is the solution of ∇γ˙s=0 on each segment. If vj+1(γ(tj))=gjvj(γ(tj)) at each internal join and vm(γ(1))=gmv1(γ(0)), where gj,gm∈U(1), then its holonomy, the scalar multiplying an initial fibre vector after transport around γ, is Holγ=(∏j=1mexp⁡(i∫γ∣[tj−1,tj]Aj))(∏j=1m−1gj−1)gm. In one unit frame defined on a neighborhood of the whole loop, write ∮γA:=∑j=1m∫γ∣[tj−1,tj]A; then the formula reduces to Holγ=exp⁡(i∮γA). If in addition γ is piecewise smooth in the sense that each rescaled segment γj(u):=γ(tj−1+(tj−tj−1)u), 0≤u≤1, is a smooth singular 1-simplex, define the finite smooth singular 1-chain cγ:=∑j=1mγj with its positive path orientation. If a finite oriented smooth singular 2-chain Σ has image in one open frame domain U and ∂Σ=cγ, then Holγ=exp⁡(i∫ΣFσ).

The piecewise C1 subdivision is understood with one-sided derivatives continuous up to each subinterval endpoint. In the final clause, each rescaled path segment must extend to a smooth map from an open neighborhood of its affine interval into S2; this is the neighborhood-extension condition for a smooth singular 1-simplex. The open frame domain U is an open subset of S2 carrying one smooth unit frame on all of U, and the image of Σ lies in U.

Facts & Assumptions

Given: The fixed direction n, helicity σ, the active rotation and the line-bundle connection convention in the Statement.

[F1]

Helicity eigenlines over the direction sphere defines the bilinear dot product u⋅w=∑jujwj, its local unit frames vσ=(eθ+iσeϕ)/2, and the connection form A=i∑jvj‾ dvj with A′=A−dχ under v′=eiχv. The projected derivative along a path is defined in the Statement.

[F2]

Exact helicity projectors in vacuum defines the transverse fibre Tn={z∈C3:n⋅z=0} and the projector Pσ; its range lies in Tn and satisfies Cnz=σz.

[F3]

Curvature and the obstruction to a global polarization basis proves the global curvature Fσ=−σωS2 for ωS2,n(X,Y)=n⋅(X×Y).

[F4]

Stokes theorem for smooth singular chains states ∫cdα=∫∂cα for finite smooth singular chains and smooth forms of the matching degree.

Proof

Given: n∈S2, σ∈{+1,−1}, an active angle α, and a path and subdivision as in the Statement.

1.1F2algebra

For z∈Lσ(n), [F2] gives n⋅z=0 and n×z=−iσz. The defining formula therefore reduces to Rn,αz=(cos⁡α−iσsin⁡α)z=e−iσαz. The phase is unchanged when α is increased by 2π because σ is an integer, and addition of angles multiplies phases, proving it is the stated character.

2.1F2step 1.1algebra

Choose a real unit vector u⊥n and put v=n×u. The real cross-product identities give ∣v∣=1, u⋅v=0, and n×v=−u, so (u,v,n) is a positively oriented orthonormal basis. In this basis the real rotation formula has matrix (cos⁡α−sin⁡α0sin⁡αcos⁡α0001), which is orthogonal with determinant one. Thus Rn,α is proper.

2.2F1F2step 1.1constructalgebra

Write a section on one chart as s(t)=a(t)vj(γ(t)). Since Pσ is the orthogonal projection onto the line spanned by the unit vector vj, the projected derivative is ∇γ˙s=(a˙+a vj†v˙j)vj=(a˙−iAj(γ˙)a)vj. Thus ∇γ˙s=0 is the scalar ODE a˙=iAj(γ˙)a, whose solution across that subpath multiplies a by exp⁡(i∫Aj). At an internal join, equality of the section on both frames gives aj+1vj+1=ajvj, hence aj+1=gj−1aj. At the end, vm(γ(1))=gmv1(γ(0)) converts the final coefficient to gmam in the starting frame. Multiplying these scalar factors gives the formula in the Statement.

3.1F1step 2.2algebra

If a frame on subpath j is changed to vj′=hjvj with hj smooth and U(1)-valued, the local connection changes by Aj′=Aj+ihj−1dhj (locally hj=eiχj this is Aj−dχj). The segment exponential acquires the endpoint ratio hj(tj)−1hj(tj−1); the adjacent transition factors change by the inverse endpoint ratios. These factors cancel at every internal join and at the identified loop endpoint. Thus the product formula is independent of the chosen local frames; no single global A is assumed.

4.1F3F4step 2.2algebra∎

For the Stokes clause, one frame is defined on the open set containing the image of Σ. By the line-integral definition and the affine reparametrizations in cγ, ∫cγA=∮γA. Since ∂Σ=cγ, the cited Stokes theorem [F4] gives ∫ΣdA=∫∂ΣA=∫cγA. The local curvature is Fσ=dA by [F3], so exponentiation gives Holγ=exp⁡(i∫ΣFσ). For paths or surfaces requiring more than one patch, the transition factors in step 2.2 are part of the holonomy; a bare integral of a nonexistent global one-form is not asserted.

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