The 3.5 keV line, reported in 2014 cluster stacks and Andromeda and read as 7 keV sterile-neutrino decay, has spent a decade deflating: absent in dwarf spheroidals and the Milky Way halo where dark matter signals should be cleanest, unseen by Hitomi in Perseus, excluded across the parameter space by blank-sky analyses, unconfirmed by eROSITA. It joins WIMPs, axions, and collider partners in ΛCDM's inventory of vanished dark matter candidates.
The model requires a dark matter particle, so every unexplained signal becomes a candidate and every null becomes a constraint rather than a verdict. The 3.5 keV episode is the pattern in miniature: an anomaly elevated by need, then dismantled by the very observations that should have strengthened it if dark matter were physical.
SCT removes the candidate at the source: there is no dark matter particle, sterile or otherwise; the gravitational phenomena attributed to it are coherence amplification of baryons (P50, P52, P53, P54). The framework therefore made the call before the data did: no decay line can scale with dark matter column density because there is no decaying column, and the observed pattern, a feature appearing in complex cluster spectra but vanishing in the clean dwarf-spheroidal tests, is precisely the signature of atomic and instrumental residuals rather than particle physics. The deflation of the 3.5 keV line is a registered SCT success of the same kind as the LUX-ZEPLIN and collider nulls.
The episode also illustrates the framework's economy: ΛCDM must adjudicate every such anomaly against an open-ended particle space, while SCT predicts a clean universal null for all decay, annihilation, and scattering signatures, an unhedged stance that each new X-ray mission tests. XRISM's resolved spectroscopy, separating atomic blends from any smooth residual, is exactly the instrument for the final word.
This is the same no-particle corollary behind the WIMP nulls and the Ω_DM/Ω_b identity. There is no need to invoke environment-dependent decay properties to keep a fading candidate alive.
The registered kill is absolute: a confirmed dark matter decay line, a 3.5 keV feature (or any other) tracking dark matter column density across clusters, halo, and dwarfs with consistent intensity scaling, would be a particle detection and would falsify SCT's coherence account outright. XRISM resolving a smooth line at the sterile-neutrino energy, irreducible to atomic transitions, in dark-matter-dominated systems is the specific near-term version.