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Physics theoremStatement: AI-adaptedProof: AI-generatedPipeline-generatedprecheck passverified 2026-10-22 (gpt-6.1-sol)
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Equality of total angular momentum integrals

Physical scope

Exact conditional identities for smooth classical electric fields and the stated vector potential in the fixed inertial SI laboratory chart. The all-space equality is restricted to source-free Schwartz vacuum packets in the specified Coulomb gauge. The finite-cube formula explicitly retains the divergence and boundary terms; no density-wise equality or universal gauge-independent split is claimed.

Statement

(a) For the real Schwartz vacuum fields and the fixed Coulomb-gauge potential defined in the preceding A-page item, let Jkin, Lcan, and Scan be the three global functionals in that definition. Then

Jkin=Lcan+Scan.

(b) More generally, let R>0 and let E,A:QR‾→R3 be restrictions of C1 maps on a neighborhood of the cube QR=[−R,R]3, let B=curl⁡A. Interpret every R3-valued volume integral below as the vector of its three ordinary real Riemann integrals, using the componentwise convention in the preceding angular-momentum Definition. The scalar integral over ∂QR means the sum of the ordinary two-dimensional Riemann integrals over its six faces, with their outward unit normals n. Define JR:=ε0∫QRx×(E×B) d3x,LR:=ε0∑i=13∫QREi(x×∇)Ai d3x,SR:=ε0∫QRE×A d3x. For each component ℓ∈{1,2,3},

(JR)ℓ=(LR)ℓ+(SR)ℓ+ε0∫QR(div⁡E)(x×A)ℓ d3x−ε0∫∂QR(n⋅E)(x×A)ℓ dS.

If the volume integrals converge absolutely in the componentwise convention of the preceding Fourier-field Definition and this boundary term tends to zero as R→∞, the corresponding whole-space identity retains the term ε0∫R3(div⁡E)(x×A) d3x. Thus the source-free Schwartz equality in (a) uses both div⁡E=0 and the vanishing surface limit; it is not an equality of local densities.

Facts & Assumptions

Given: The fields E,A,B and functionals of the statement, the fixed positive orientation and origin, and (for part (b)) a finite cube QR.

[F1]

The global functionals are defined by Jkin=ε0∫x×(E×B), Lcan=ε0∑i∫Ei(x×∇)Ai, and Scan=ε0∫E×A; their packet fields are Schwartz. (Coulomb-gauge canonical and kinetic integrals)

[F2]

For these packets B=curl⁡A and div⁡E=0; E,A,B are smooth Schwartz fields. (Classical transverse Fourier amplitudes)

[F3]

The component formula for the right-handed cross product is (u×v)i=∑j,kϵijkujvk, and its products are bilinear; every repeated coordinate index in the proof ranges from 1 to 3 and is summed. (The cross product in R3)

Proof

1.1F3algebra

For i∈{1,2,3}, expand the cross product by [F3]: (E×curl⁡A)i=∑j,k,m,nϵijkϵkmnEj∂mAn =∑jEj∂iAj−∑jEj∂jAi. Indeed, if either index pair repeats, both sides of ∑kϵijkϵkmn=δimδjn−δinδjm are zero. For distinct i,j, only the remaining coordinate k contributes; the left side is +1 when (m,n)=(i,j), −1 when (m,n)=(j,i), and zero otherwise, exactly as on the right. Multiplying by ε0∑m,iϵℓmixm and summing over i,m makes the first term exactly (LR)ℓ and leaves (JR)ℓ−(LR)ℓ=−ε0∑m,i,j∫QRϵℓmixmEj∂jAi d3x.

2.1step 1.1F3F4algebra

For each fixed pair of the other coordinates, the one-dimensional FTC in [F4] applied to xmEjAi gives ∫QRxmEj∂jAi=∫∂jQRnjxmEjAi dS−∫QR(δjmEj+xm∂jEj)Ai d3x; Riemann-Fubini in [F4] justifies integrating those section identities over the two remaining coordinates and summing faces. Substitution in step 1.1 gives the volume term ε0∫QR(div⁡E)(x×A)ℓ, the surface term −ε0∫∂QR(n⋅E)(x×A)ℓ, and the remaining volume term ε0∫QR(E×A)ℓ=(SR)ℓ. This is exactly (b).

3.1step 2.1F1F2F4∎

For the Schwartz packets, every volume term in (b) converges absolutely by the estimates in the definition of Jkin,Lcan,Scan. On each face of QR, ∣x∣≥R; choosing Schwartz decay order N≥3 for both E and A bounds the surface integrand by C(1+∣x∣)−2N+1, and the total face area is 24R2. Hence the boundary term tends to zero. By [F2] the divergence term vanishes identically. Taking R→∞ in the finite-cube identity (b) proves (a).

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