Hosting versus Deriving the Born Rule in Registration Theory: A Conditional Theorem, Native Quadratic Invariants, and Obstructions

Abstract

This status report asks whether Registration Theory (RT) derives the qubit Born rule, P(+) = cos²φ, from its own deterministic registration dynamics, or only hosts a construction that reproduces it. RT's canonical finite model is the four-node adaptive consequence-registration field (ACRF-4).Main results:A conditional Born theorem. If the preparation–measurement map supplies (C1) an additive seed, (C2) a fine-state distribution equal to the planar shadow of the uniform 2-sphere, and (C3) a consequence angle locked to twice the preparation–apparatus angle, then ACRF's exact receiver seed yields P(+) = cos²φ. Condition (C2) is shown to be necessary (Cramér–Wold).Native quadratic structure. RT's bilateral phase invariant ζ satisfies tr(P̂_U P̂_V) = (1 + Re ζ²)/2 = cos²Δ, a gauge-invariant projector overlap with the Born form, and the angle doubling follows from RT's sign-gauge quotient. Square-root ledger coordinates realize a Pythagorean split, S = s cos²θ and T = s sin²θ.Obstructions:At detector readiness, the receiver seed is exactly bilinear and does not depend on the coordinate that sets the native Born weight.Phase-only sufficiency fails by explicit counterexample: identical ζ with opposite seed signs.Tangent isotropy is broken by the same boundary couplings that produce the seed.Readiness restricts the seed-visible fine state to a circle, which gives the wrong probability law.A full so(3) commutator algebra generated by retained history is generic and does not by itself select the spherical measure.Conclusion: RT currently hosts, but does not derive, the Born rule. The report identifies the single missing object, a preparation–measurement map, and lists preregistered tests, including a recorded prediction of failure for the isotropy test. It also states one falsifiable consequence: small deviations from Born frequencies concentrated near the outcome threshold.Every claim is labeled exact [E], numerically verified [V], or reported from project audits [R]. The accompanying Python script (rt_born_checks.py, NumPy, fixed seeds) reproduces every [V] claim.Computations, adversarial checks and drafting were assisted by AI language models. The author is responsible for the content.