Harmonic Scale Framework

This document introduces the Harmonic Scale Framework (HSF), a band-agnostic resonant-response theory for GHz–THz spectroscopy and ultralight field searches. HSF models the observable R(f)R(f)R(f) as a small set of coupling-weighted resonances (ESR, electron cyclotron, plasma; optionals like upper-hybrid) using a dimensionless Lorentzian basis (“Harmonic Scale”) that stabilizes fits from kHz to THz and naturally accommodates IF/down-conversion. Rather than explaining peaks in isolation, HSF performs closure across channels: frequencies, widths, and amplitudes must satisfy coherence and scaling laws with magnetic field, electron density, and polarization. Competing hypotheses are compared on the same data—Track A (direct narrow line; ALP/dark photon-like) vs. Track B (scalar modulation of constants with sidebands)—using ΔBIC → Bayes factors. We provide falsifiable predictions (B- and density-scaling, polarization flips, sideband ratios) and two illustrative HSF particles: an ultralight scalar χ\chiχ (mass-portal modulation) and a dark vector VXV_XVX with longitudinal plasma mixing. The package includes practical YAML sketches and data formats (CSV f_Hz,R) to enable reproducible analyses, parameter estimation (B, nen_ene, effective couplings), and competitive limits without assuming new physics a priori—while remaining sensitive to it.