Dark-Matter Hopfion Detection: Protocols for the H=0 Soliton Dust

The Hopf soliton programme identifies dark matter with the H=0 sector of the programme's field n: M → S² — a pressureless dust of field-topology defects with mass ~ 0.89 MeV (Paper LXVII). H=0 hopfions are electromagnetically weak: zero magnetic moment, polarisability α_E ~ 10⁻⁴³ m³/T² (too small for direct B-field detection by ~30 orders of magnitude), no colour charge. We catalogue the experimental landscape and identify four plausible detection strategies: (P1, primary) a 0.89 MeV line in WIMP direct-detection electron-recoil data — re-analysis of existing XENONnT/LZ/SuperCDMS data; (P2) sub-MeV polarised scattering at JLab or a dedicated 5-MeV Mott table; (P3) stellar cooling rate anomaly at T ≳ T_fo ~ 0.15 keV — already constrains σ_DM-e^emission < 10⁻⁴² cm²; (P5) collective-mode excitation in condensed-matter hopfion materials — overlaps Paper CXXVI Protocol E3. One nominal protocol is informative-negative: (P4) nuclear resonance — no theoretical coupling exists in the current programme framework; included only as a caveat against future re-derivation. Direct B-field detection (the polarisability route from Paper CXXV §4.4) is excluded by ~30 orders of magnitude and is not pursued. P1 is the central prediction, achievable by existing experiments via analysis changes (no new apparatus); P2, P3, P5 give independent cross-checks at varying timelines (1-2 yr, astrophysical, 6 months). Keywords: dark matter, direct detection, Hopf soliton, H=0 sector, sub-MeV dark matter, stellar cooling, electron recoil, 0.89 MeV, XENONnT, LZ