Friday, September 8, 2017

LHC and XENON-100 Further Constrain Dark Matter Parameter Space

A review of the data from the Large Hadron Collider's ATLAS and CMS experiments shows that Higgs portal dark matter (or any other kind of dark matter that the LHC could detect) is pretty much completely ruled out in mass ranges from near zero to the multiple TeV range. There is one little blip at about 2.75 TeV in the data, but not significant enough to be worthy of much interest (particularly because this mass range is already strongly disfavored for stable dark matter candidates).

Meanwhile the Xenon-100 direct dark matter detection experiment has basically ruled out "Bosonic Super-WIMPs" at the heavy end of the warm dark matter spectrum. The abstract (not in blockquotes because it messes up the formatting):

"We present results of searches for vector and pseudo-scalar bosonic super-WIMPs, which are dark matter candidates with masses at the keV-scale, with the XENON100 experiment. XENON100 is a dual-phase xenon time projection chamber operated at the Laboratori Nazionali del Gran Sasso. A profile likelihood analysis of data with an exposure of 224.6 live days × 34\,kg showed no evidence for a signal above the expected background. We thus obtain new and stringent upper limits in the (8125)\,keV/c2 mass range, excluding couplings to electrons with coupling constants of gae>3×1013 for pseudo-scalar and α/α>2×1028 for vector super-WIMPs, respectively. These limits are derived under the assumption that super-WIMPs constitute all of the dark matter in our galaxy."

The most promising mass range for warm dark matter is about 2 keV to 8 keV, so this study rules out heavier candidates. Of course, only if they are bosons, rather than fermions, and only if they have any electroweak couplings as opposed to being "sterile". In principle, would could imagine a tiny fractional weak force coupling, but there is absolutely nothing in the empirical evidence to support a weak force coupling that existed with a weak force coupling constant that was much more than a million times weaker than the weak force coupling constant of every other Standard Model particle that has weak force interactions.

A truly sterile dark matter candidate is problematic because it can't explain why ordinary matter and dark matter distributions are so tightly correlated, something that it is increasingly clear that unmodified gravity alone can't cause. But, there is also no empirical or theoretical motivation for an ultra-small weak force coupling for a class of matter that would vastly exceed all other matter in the universe by mass or particle count.

A new paper also strongly constrains dark matter that only interacts with right handed up-like quarks (which the authors call "Charming Dark Matter"). Another paper looks at how to more rigorously distinguish between a single component dark matter scenario and one with more than one component - early simulation data strongly disfavored multi-component solutions but didn't necessarily rigorously proof that they were ruled out.

One by one, experimental and astronomy observation data points continue to narrow the parameter space for dark matter particles to essentially zero, leaving modified gravity theories, most likely due to infrared quantum gravity effects, as the only possible explanation for dark matter phenomena.

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