Weakly interacting massive particles, a dark matter hypothesis inspired by supersymmetry theories, has long ago been falsified.
The failure of direct detection experiments (in mass ranges from 250 MeV to more than 10 TeV) shown below is matched by lack of any signs of such particles in particle accelerators up to hundreds and thousands of GeV, and by the dynamics of inferred dark matter in galaxies.
Image from here. The dotted blue line labeled Z portal Cx=1 in the chart below is basically equivalent to the cross-section of interaction with nucleons of ordinary Standard Model neutrinos. A femtobarn (fb) is 10^-39 cm^2. An attobarn (ab) is 10^-42 cm^2. A zeptobarn (zb) is 10^-45 cm^2. A yoctobarn (yb) is 10^-48 cm^2.
The latest experimental limits on WIMP dark matter from LZ (arXiv:2207.03764). The parameter space above the line is excluded. Note the scale on the y-axis bearing in mind that the original expectation was for a cross section around 10-39 cm2, well above the top edge of this graph.
LZ is a merger of two previous experiments compelled to grow still bigger in the never-ending search for dark matter. It contains “seven active tonnes of liquid xenon,” which is an absurd amount, being a substantial fraction of the entire terrestrial supply. It all has to be super-cooled to near absolute zero and filtered of all contaminants that might include naturally radioactive isotopes that might mimic the sought-after signal of dark matter scattering off of xenon nuclei. It is a technological tour de force.
The technology is really fantastic. The experimentalists have accomplished amazing things in building these detectors. They have accomplished the target sensitivity, and then some. If WIMPs existed, they should have found them by now.WIMPs have not been discovered. As the experiments have improved, the theorists have been obliged to repeatedly move the goalposts. The original (1980s) expectation for the interaction cross-section was 10^-39 cm^2. That was quickly excluded, but more careful (1990s) calculation suggested perhaps more like 10^-42 cm^2. This was also excluded experimentally. By the late 2000s, the “prediction” had migrated to 10^-46 cm^2. This has also now been excluded, so the goalposts have been moved to 10^-48 cm^2. This migration has been driven entirely by the data; there is nothing miraculous about a WIMP with this cross section.
From Triton Station.
9 comments:
There Are No WIMPs
so far
They are ruled out. Not "so far". There are dark matter candidates that aren't ruled out, but WIMPs are ruled out.
if lx has a detection what could it be
@neo
We'll see when and if it happens. Previous false alarms like Xenon1T were probably due to background interactions that the experiment failed to rule out.
At this point, the cross-sections of interactions not ruled out are so low, millions to billions of times weaker than the weak force only cross-section of interaction of a neutrino, and there is a complete absence of theoretical motivation for that kind of DM candidate. If there is DM it would make much more sense for it to have a zero cross-section of interaction with ordinary matter apart from gravitational interactions. But, as my many prior posts have shown, the available galaxy dynamics and lensing data pretty soundly rules out that possibility and even self-interacting dark matter that only interacts with other dark matter doesn't really solve the problem. The tightness of fit between inferred DM distributions and ordinary matter distributions is simply to great to arise without some kind of cross-section of interaction between DM and ordinary matter that is stronger than gravity alone if you use the Newtonian approximation of gravity in galaxies and galaxy clusters the underlies all DM particle theories.
A WIMP in the strict sense, interacts via the weak force (implying a fm cross-section of interaction of 10^-39, and has a mass scale of roughly 0.1 GeV to 10,000 GeV at the greatest extremes. Certainly, this is true for supersymmetric WIMP candidates. There is no more room for them in the data.
We can't give up yet! There are still NIMPs (neutrino interacting massive particles).
Never seen the acronym NIPS before.
It's my coinage, meant to be mildly humorous. You're right, it has been obvious for a while that weak interaction limits were excluding WIMPs, and about all that's left for dark matter are tiny stable black holes and particles that only couple to neutrinos. The difficulties with finding limits on neutrino interactions are obvious. You can do back of the envelope calculations with SN1987A neutrinos and models of dark matter distributions, but it isn't very limiting. Scattering of ultra-high energy neutrinos might say something, but getting statistics is going to take quite a while, and it needs an awful lot of modeling work.
Almost all of the parameter space for particles that interact via the weak force has been ruled out. Almost all of the PBH parameter space has been ruled out (arguably all of it), and so has all of MACHO parameter space. Collisionlesss DM that interacts only via gravity is pretty much ruled out (because there is too tight a correlation with baryonic matter). Almost by definition, DM doesn't interact via the strong or EM forces. High energy neutrinos as DM were ruled out long ago. Creatively for new DM candidates in seemingly inexhaustible, but the collective literature paints a very grim picture for DM particle theories taken collectively.
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