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A fixed Cartesian polarization is not a global transverse helicity frame
Statement refuted
Let be the standard coordinate basis of . The constant Cartesian circular vectors , for , form a transverse helicity frame for every nonzero momentum direction; consequently this fixed pair supplies a momentum-independent polarization factor on the transverse one-photon space.
Statement references
Facts & Assumptions
Given: Countable Choice and the transverse helicity setting below; the additional full Choice premise [A1] is used only for the rotation-generator conclusion in step 3.1.
For [F3] and step 3.1, assume the Axiom of Choice: every family of nonempty sets has a function selecting a member of each set. The fixed-pair refutation in steps 1.1–2.1 uses only the Countable Choice setting of [F4]–[F5]. The Axiom of Choice
Each helicity fiber lies in the transverse plane . Transverse one-photon space and helicity projectors
The standard first Chern number of is , and no global smooth unit helicity section exists. Helicity line bundles have nonzero Chern number
Under [A1], fix and with . On , put and , with the cross product extended complex-linearly. The self-adjoint Stone generator of the rotation action , with convention and , , restricts on to . Its orbital and spin terms generally do not separately preserve transversality. The full Choice premise is required by this supplier's Stone-theorem application. Transverse rotations preserve helicity and generate total angular momentum
The momentum domain is with , and consists of equivalence classes satisfying for -almost every . At each , the transverse fiber is , using the complex-bilinear extension of the real dot product. Transverse one-photon space and helicity projectors
Under Countable Choice, every Borel subset of is Lebesgue measurable; closed coordinate boxes have measure equal to the product of their side lengths; is a measure on the Lebesgue sigma-algebra; and measures are monotone on measurable inclusions. Countable Choice is already part of the transverse-space setting in [F4]. Assuming countable choice, every Borel subset of is Lebesgue measurable A box in with parameters is Lebesgue measurable of measure , whichever of its faces are included Assuming countable choice, is a sigma-algebra containing every elementary set and is a complete measure extending elementary volume Measures are monotone
Counterexample
Given: Countable Choice, a nonzero momentum , and the constant vectors in the Statement; additionally [A1] for step 3.1.
To make the fixed-pair factorization claim precise, let , with norm . For each define by , and define by . The two fixed vectors are Hermitian-orthonormal, so is an isometry into the ambient vector-valued space. The fixed-pair factorization claim tested below is that this map takes values in and is unitary onto it; pointwise, it claims that the same two vectors supply each transverse fiber .
Take with . Then for either , so neither fixed vector lies in the transverse plane . By [F1], neither can belong to the corresponding helicity line at this momentum.
Independently, [F2] excludes any global smooth unit helicity eigenvector, even if the polarization vector is allowed to depend on momentum. Thus a smooth global helicity gauge cannot repair the fixed-frame claim.
Let , , and . For , , so . For every coordinate displacement from has absolute value less than , so . The ball is open: if , then the ball of radius about lies in by the triangle inequality. It is therefore Borel and Lebesgue measurable by [F5]. The box-volume formula and measure monotonicity in [F5] give . The triangle inequality gives on , so there. Integrating these inequalities yields . Thus belongs to . For every , and , since . Thus fails the transverse condition on the positive-measure set ; in particular, does not define a map from into , and cannot be the proposed unitary factorization.
The displayed fixed pair therefore is not a transverse helicity frame on all momentum directions, and the explicitly defined fixed-pair map fails to factor through the transverse one-photon space. The Chern obstruction separately excludes a global smooth helicity frame even when vectors are allowed to depend smoothly on momentum. This refutes the statement.
Under the additional full Choice premise [A1], the rotation theorem [F3] also identifies the precise limitation of separating orbital and spin terms: their displayed differential expressions need not individually send the transverse domain into itself, whereas their sum does. Hence those separate restrictions do not give independent operators from to on the common transverse domain. This refutes a decomposition by those particular restrictions; it does not rule out arbitrary Hilbert-space tensor-product isomorphisms.
Depends on
The Axiom of Choice
Transverse one-photon space and helicity projectors
Helicity line bundles have nonzero Chern number
Transverse rotations preserve helicity and generate total angular momentum
Assuming countable choice, every Borel subset of is Lebesgue measurable
A box in with parameters is Lebesgue measurable of measure , whichever of its faces are included
Assuming countable choice, is a sigma-algebra containing every elementary set and is a complete measure extending elementary volume
Measures are monotone