Here in the Era of (Attempted) Dark Matter Detection, new results just keep coming in. Some are tantalizing, some simply deflating. Count this one in the latter camp.
The XENON100 experiment is a detector underneath the Gran Sasso mountain in Italy (NYT article). It’s a very promising experiment, and they’ve just released results from their most recent run. Unlike some other recent announcement, this one is pretty straightforward: they don’t see anything.
Here we see the usual 2-dimensional dark matter parameter space: mass of the particle is along the horizontal axis, while its cross-section with ordinary matter is along the vertical axis. Anything above the blue lines is now excluded. This improves upon previous experimental limits, and calls into question the possible claimed detections from DAMA and CoGeNT. (You can try to invent models that fit these experiments while not giving any signal at XENON, but only at the cost of invoking theoretical imagination.) See Résonaances or Tommaso Dorigo for more details.
No need to hit the panic button yet — there’s plenty of parameter space yet to be explored. That grey blob in the bottom right is a set of predictions from a restricted class of supersymmetric models (taking into account recent LHC limits). So it’s not like we’re finished yet. But it is too bad. This run of XENON had a realistic shot of actually finding the dark matter. It could be harder to detect than we had hoped, or it could very well be something with an extremely small cross-section, like an axion. The universe decides what’s out there, we just have to dig in and look for it.
It seems to me there is now a distinct possibility that sterile neutrinos could be dark matter, rather than something supersymmetric or axionic, if one takes the recent hints of excitement from the MINOS collaboration at face value…
Question: how do sterile neutrinos jive with cold dark matter models — presumably, they aren’t very cold?
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I found Mark Datter!: http://www.facebook.com/people/Mark-Datter/569632569
sorry
My arm-chair speculation money is on dark matter being the new aether. (At least concerning exotic DM–offer excludes neutrino and baryonic “stuff”.)
I’d like the theory of antimatter quark nuggets to be true, if only because capturing microscopic multi-ton antimatter chunks zipping through the solar system might eventually become feasible — and useful as an energy source.
If you look at a higher-dimensional parameter space, is DAMA still such an outlier?
Two words – Cooperstock, Tieu.
-drl
@5
You need to listen to Feynman.
Doesn’t matter what you would like. Nature is what it is.
Seems like the Xe Leff issue that caused all that ruckus last year is still unresolved. They don’t really seem to address it in the current paper.
Extrapolating is still extrapolating. Model-dependent predictions are still model-dependent.
(And to boot, the model they’re based on – SUSY – is much less well-motivated than the evidence for dark matter)
My takeaways:
weakly-interacting massive particle (lowercase) – still very much possible.
SUSY Weakly-Interacting Massive Particle (uppercase) – less likely than before.
MONDers – not much of a victory.
Thoughts?
It’s disappointing, but not discouraging. Look at LIGO/VIRGO. Now That is discouraging, with no detection of grav waves after a decade of science runs, yet they continue to place limits having seen Nothing. Sort of like the sparticle people:”They must be just a bit heavier”, ad nauseam.
What is disturbing here is that all the prior searches are effectively excluded by one. No Way. Regardless of it’s signal to noise ratio being the highest of all the others, I think the jury is still out, & it would be `CoGent’ to keep an open mind. As Shelly Glashow admonished the stringers,
“Please heed our advice that you too are not smitten; The book’s not finished, the last word is not Witten.”
Or there could be some weird crap like MOND or something going on, and no dark matter.
Still waiting for some religious website to state: “Search for answered prayer still negative.’
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This is a bit of a tangent, but is the recent Fukushima disaster going to put enough radioactive Xe and Kr isotopes into the atmosphere to make future bigger Xe experiments difficult?
Sterile neutrino, as I understand sterile neutrinos are warm dark matter candidates and WDM
is no longer favored.
Is dark matter the new Phlogiston (or aether as Cody suggested)? Observable phenomena that are real, but the theoretical postulated mystery substance to explain the phenomena is just wrong.
The evidence for physical dark matter objects appears to be quite strong.
But do these dark matter objects have to be subatomic particles?
Black holes of about 1 solar mass formed in the early universe are stable against Hawking radiation and do not conflict with metal abundance constraints.
They are nonbaryonic, stable, and quite fundamental objects that interact with normal matter gravitationally, but do not emit a lot of radiation if undisturbed in the galactic halo.
Should we not pay some consistent lip service, or even some serious thought, to such a natural dark matter candidate? After all, there is considerably more observational evidence for “primordial” black holes than there is for WIMPs, sparticles, axions, sterile neutrinos, etc.
Albert Z
Goodbye, Ruiz et al.
http://xenon.astro.columbia.edu/images/XENON_sensitivity_w1T.png
Hello, Buchmueller et al.
Let’s see now. What characteristics of Invisible DM have we found so far, Watson?
1. Invisible DM strongly in evidence around all galaxies and exerts a powerful gravitational influence on the rotational speed of every part of those galaxies.
2. Cannot be found anywhere near massive bodies such as planet surfaces, let alone deep mines.
This is a little bit more complex than a 2 + 2 brain teaser.
Perhaps every particle of Invisible DM in the universe is emitting tiny gravitational waves from Lisa Randall’s tetra space ‘brane’ and ‘bulk’ to help us all keep our baryonic feet on the baryonic ground, in a le Sage type of way.
Just a non peer reviewed thought.
“Black holes of about 1 solar mass formed in the early universe are stable against Hawking radiation and do not conflict with metal abundance constraints.
They are nonbaryonic, stable, and quite fundamental objects that interact with normal matter gravitationally, but do not emit a lot of radiation if undisturbed in the galactic halo.”
If such objects were to make up most of the dark matter, they would have a much stronger microlensing signal than is observed.
Good idea, but ruled out by observations.
Personally I suspect dark matter to be some conceptual problem in the foundations of physics.
As an example of the type of problems i have in mind consider Lorentz Symmetry, we believe Nature obeys this symmetry, but is that really the case? Perhaps LS is not really an universal symmetry of Nature but rather a consequence of the way we observe it. There could be other fields/entities out there which do not obey LS and which are too fleeting and chaotic to interact with normal matter in any other way then by gravitation (quantum interactions mediated by particles require a certain spatio-temporal synchronization which could very well be impossible for fields violating Lorentz invariance).
Not really surprising that no Dark Matter was found. It’s pretty clear that it’s spectacularly absent from our part of the cosmos. If it were here it would affect everything from the orbits of planets and satellites to the paths of laser beams. Considering that only 5% or so of the universe is ‘normal’ matter (according to the theory) isn’t it just a touch bizarre that we’re surrounded by nothing but that?
My guess is that there is no ‘Dark Matter’ or ‘Dark Energy’ – a much more credible explanation would be variations in ‘constants’ such as gravity, lightspeed etc etc.
@20 Phillip Helbig: “If such objects were to make up most of the dark matter, they would have a much stronger microlensing signal than is observed.
Good idea, but ruled out by observations.”
Because we know what microlensing looks like, and would know it when we see it? Seriously, what’s the object weight limit that we’ve got from experiment?
The current generation of physicists will of course never consider any null result as evidence against susy. Progress only happens from funeral to funeral.
Dark matter is like Count Dracula. It will take more than a few nails in the coffin to put this neo-aether idea to rest. Fortunately, there are now three studies linking the temperature of a test mass to its gravitational weight. These studies suggest the possibility that luminosity is the source of gravitational attraction. Astronomers all know that luminosity emanates from all gravitationally bound bodies in the universe such as binary stars, planetary systems, galaxies and clusters. My studies show a 1.9%, 8.9%, 9.6% and a 16% increase in the weight of the test mass when these test masses were placed between a 1000 W hot source and a cold source. Such unexpected anomalous results challenge the principle of equivalence upon which General Relativity depends and Einstein’s interpretation of E = mc^2. But go a ahead and ignore them. Maybe someday they will find that dark matter (and dark energy).
http://vixra.org/abs/0907.0018
http://arxiv.org/abs/0803.1730