Physical Nature and Minimal Identity of the Neutrino Carrier

Neutrino carrier ARC and HNL prediction 15/18 This paper determines the physical nature and minimal terminal identity of the neutrino carrier within the two source-qualified vectorlike-joint sectors completed by PCR‑5E. The preceding PCR papers establish the neutrino oscillation target, source-first carrier universe, simultaneous survivor residue, compatible role occupancy, standing-carrier quotient, and the joint target extensions. PCR‑6 addresses a distinct question: within one accepted realization, which structures are internal standing spectral sectors, and which structure is independently complete as the terminal carrier? The analysis constructs an activity-reduced internal-sector groupoid natural over each completed moduli groupoid. For the vectorlike-joint source, the exact mass map has three nondegenerate light spectral projectors and a threefold-degenerate heavy eigenspace. The light projectors remain standing-distinct under the retained oscillation and charged-current boundary traces. On the heavy subspace, every target-admitted witness is equivariant under the lawful \(U(3)_H\) action and therefore descends to a single rank-three heavy projector. The standing spectral core is consequently \[ \mathrm{SpecCore}(X)=\{S_1,S_2,S_3,S_H\}, \]consisting of three nondegenerate light sectors and one rank-three degenerate heavy sector. This is a \(3+1\) spectral structure within one carrier—not four independent terminal particles or four separate carriers. Terminal carrier identity is evaluated only after the complete source, continuation, matching, and physical witness interfaces have been activated. The paper proves that no individual light sector, proper light aggregate, heavy sector, proper light-heavy aggregate, or isolated relation possesses a complete terminal signature. A source-support exhaustion theorem then shows that every independently eligible, terminally complete candidate capable of entering a complete one-apex assignment must contain the full deletion-essential support of the parent realization and is therefore lawfully equivalent to the source-connected parent carrier. A fresh within-realization Role-Occupancy Closure calculation yields one live terminal bearer class and one compatible assignment orbit: \[ |\mathrm{TermCar}(X)|=1. \]The terminal object is classified as a local hybrid neutral-fermion carrier with a vectorlike Dirac mass-map core, common charged-current boundary incidence, and target-essential matching and continuation structure. The one-carrier result is branch-stable across the two completed sectors. The carrier core is common to the bounded-accidental and exact-global \(B-L\) branches, while their full minimal identity packets remain distinct because their symmetry and conjugation data differ. The conclusion is deliberately bounded. The paper establishes one terminal carrier within each accepted realization of the specified vectorlike-joint sectors. It does not select a unique PCR‑5E realization, prove a universal one-carrier theorem for every possible neutrino architecture, identify four terminal particles, or determine a unique ultraviolet completion. The continuum of cross-realization possibilities and unresolved parent sectors remain intact.