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Suppose that current and new forthcoming dark matter direct detection experiments find no evidence of Dark matter events and exclude interactions of hypothetical DM particles (like LSP or similar) in the cross-section range 10⁻⁴⁴-10⁻⁴⁸ cm². What would it mean for SUSY? What would it mean for "new physics" in the weak sector?

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    $\begingroup$ It means that the current "easy" model for how dark matter interacts (weak boson exchange) is bogus, but we know there is something to be explained, so people will keep looking. Axions or something. $\endgroup$ Commented Mar 3, 2014 at 22:02
  • $\begingroup$ BTW, that "Dark Matter lower wall" is customarily called the "neutrino floor" or more accurately the "neutrino fog" $\endgroup$
    – rfl
    Commented Sep 22, 2021 at 19:14

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SUSY and new physics at the Weak scale will be less likely, but not completely ruled out.

In principle, SUSY has so many tuneable parameters that it can not be ruled out completely. Fine. Little green men on Mars also can't be ruled out completely, and yet nobody thinks they are real, so that does not have to be a deal breaker as far as hypotheses go.

The original proposal of a WIMP (Weakly Interacting Massive Particle) would have it to interact via Z-bosons at tree level, just like neutrinos do, but more massive. Those kinds of cross-sections (in the ball park of 10^-32cm^2) were ruled out already in the 1990s. In addition to SUSY and some other more specialized models, two basic benchmarks are probed by current experiments: Z-exchange at the loop level (i.e. through a box diagram) or Higgs-mediated couplings ("Higgs portal"). Both those scenarios are still well and alive given current constraints. However, pushing those current constraints down by another three orders of magnitude to the signal from atmospheric neutrinos would render these couplings unlikely as well.

Unraveling the nature of dark matter is just too big a problem that one could leave this well-motivated parameter range unprobed. This is in particular true since it is experimentally accessible in relative simple and cheap ways, just by scaling current experiments (LZ/XENONnT, PICO, eventually DarkSide) up once more. The prudent thing to do is to push ahead and probe this parameter space, while at the same time, expanding technology to probe different kinds of models --- and that is exactly what is happening in this are of research right now.

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Short form: 1) Waffle with more and more of less and less as Yukawa potentials. 2) Do what everybody did to "explain" the Pioneer anomaly, the Fifth Force, absence of proton decay, and Gran Sasso's "superluminal" neutrinos: parameterize! There is nothing sacred about quantum gravitation or SUSY other than they employ vast numbers of people who cannot demonstrate empirical relevance.

Let's play empiricist not theorist, arXiv:1310.4009, 0906.0668. Milgrom acceleration not dark matter to satisfy the Tully-Fisher relation. Now we need free angular momentum. If we assume the vacuum is achiral isotropic toward hadrons (fermionic quarks), then parity violations, symmetry breakings, chiral anomalies, Chern-Simons repair of Einstein-Hilbert action. OK, the vacuum is trace chiral anisotropic toward matter (but not boson photons). Then, Noetherian coupling of exact vacuum isotropy to angular momentum conservation leaks for matter as MoND's 1.2×10^(-10) m/s*2 Milgrom acceleration.

This is no improvement unless we can measure said (crackpot scheme) vacuum trace chiral anisotropy toward matter. Einstein-Cartan-Kibble-Sciama gravitation contains chiral spacetime torsion. Spacetime curvature is a racemic subset (re Ashtekar). Opposite shoes embed within chiral vacuum (mount a left foot) with different energies. They vacuum free fall along non-identical minimum action trajectories, exhibiting Equivalence Principle violation. A pair of literal shoes won't do it, arXiv1207.2442.

Crystallography's opposite shoes are visually and chemically identical, single crystal test masses in enantiomorphic space groups, e.g., P3(1)21 vs. P3(2)21 alpha-quartz. OK, mount eight test masses in the Eötvös balance. 40 grams net as 8 single crystal test masses compare 6.68×10^22 pairs of opposite shoes (pairs of 9-atom enantiomorphic unit cells, the test mass array cube's opposite vertical sides).

Euclid did a perfect job. Cartography tells us Euclid is incomplete. Newton did a perfect job, but then relativity and quantum mechanics. Quantum gravitation and SUSY did perfect jobs, all of it irrelevant to empirical prediction. When things fail they were meant to fail. Look elsewhere consistent with prior observation.

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