Relativistic Shedding (RS) as Threshold Emission into Hidden Sectors(V5)

Relativistic Shedding (RS) is presented as a laboratory-search framework for threshold‑modulated emission into hidden‑sector eigenmodes, designed to produce falsifiable, on/off (ABAB) signatures rather than relying on absolute-rate predictions. This Version 5 consolidates the project into a “complete standard” reference: it explains why an LDMX-style missing‑momentum implementation initially appeared ideal (clean threshold bracketing and systematic cancellation), then shows—using dispersion and scale arguments—why that specific mapping does not align with the relevant in‑medium eigenmode conditions for the intended parameter regime. The focus then pivots to dielectric/slow‑wave and resonant receiver (LSW‑class) laboratory architectures, where RS becomes a unique, stand‑alone threshold handle: the signal is a narrowband regenerated response that appears only when a physically defined phase‑velocity/dispersion threshold is crossed, with multiple built‑in falsifiers (receiver detuning, shielding/leakage checks, geometry/polarization swaps, thickness/material scaling, and ABAB reversibility). Version 5 includes expanded derivations (in‑medium mixing, transverse vs longitudinal transmission, thin‑wall/off‑shell extensions), a quantitative sensitivity example using radiometer‑limited detection, and an updated constraints/context section reflecting modern cavity/LSW progress.