So apparently I just took an unscheduled blogging hiatus over the past couple of weeks. Sorry about that — it wasn’t at all intentional, real life just got in the way. It was a fun kind of real life — trips to Atlanta, NYC, and Century City, all of which I hope to chat about soon enough.
Anything happen while I was gone? Oh yeah, dark matter was not discovered. More specifically, the LUX experiment released new limits, which at face value rule out some of those intriguing hints that might have been pointing toward lighter-than-expected dark matter particles. (Not everyone thinks things should be taken at face value, but we’ll see.) I didn’t get a chance to comment at the time, but Jester and Matt Strassler have you covered.
Let me just emphasize: there’s still plenty of room for dark matter in general, and WIMPs (weakly interactive massive particles, the particular kind of dark matter experiments like this are looking for) in particular. The parameter space is shaved off a bit, but it’s far from exhausted. Not finding a signal in a certain region of parameter space certainly decreases the Bayesian probability that a model is true, but in this case there’s still plenty of room.
Not that there will be forever. If dark matter is a WIMP, it should be detectable, as long as we build sensitive enough experiments. Of course there are plenty of non-WIMP models out there, well worth exploring. But for the moment Nature is just asking that we be a little more patient.
Though at some point, direct detectors will run into the cosmic neutrino background and make it even harder to look for WIMPs.
@ Sean Carroll: “The parameter space is shaved off a bit, but it’s far from exhausted. … Not that there will be forever. If dark matter is a WIMP, it should be detectable, as long as we build sensitive enough experiments. Of course there are plenty of non-WIMP models out there, …”
*God* can never be found. Anything that can never be found becomes the Almighty instantly. Henry Gee, a senior editor at Nature penned a piece entitled, “Science: the religion that must not be questioned (http://www.theguardian.com/science/occams-corner/2013/sep/19/science-religion-not-be-questioned?commentpage=1 )”. His conclusion is, “Why is this? The answer, I think, is that those who are scientists, or who pretend to be scientists, cling to the mantle of a kind of religious authority. And as anyone who has tried to comment on religion has discovered, there is no such thing as criticism. There is only blasphemy.” Yet, the current status of particle physics goes way beyond the Gee’s description.
Recently (about a week ago), a new measurement for the Electric Dipole Moment of the Electron (by The ACME Collaboration, http://arxiv.org/pdf/1310.7534v1.pdf ) was published. It claims that it sets strong constraints on new physics (SM extensions) associated with T-violating interactions at the TeV [up to 30 Tev] energy scale. This *not finding* report vindicates the earlier claim that SUSY (with s-particle) must reside above 30 Tev..
Well, a *stable* particle resides above 30 Tev does not truly play any significant part in *this universe*. But, don’t worry; there is *Multiverse*. So,
a. There is solid evidence that there is dark mass.
b. SUSY (with s-particles) is the best candidate for the dark matter.
c. The *not finding* of SUSY and dark matter is because that they reside above, at least, 30 Tev..
d. The argument that a stable particle of 30 Tev is very much disconnected to *this universe* is not an issue at all as there is the Multiverse.
Thus, these three (Dark matter, SUSY and Multiverse) form a great Trinity. The only problem with this great Trinity is that the dark mass is a vital part of *this universe*. There are two ways to crack this great Trinity.
i. There is now the Planck data (dark energy = 69.2; dark matter = 25.8; visible matter = 4.82). When it can be fully accounted for by a model (such as, the Iceberg Model. See http://physicsfocus.org/katie-mack-space-station-ams-detector-has-not-found-dark-matter-despite-what-some-media-reports-say/#comment-3232 ), the dark matter issue is resolved.
ii. When the multiverse bubbles are proved to be all connected (that is, forms a single bubble, see http://blog.vixra.org/2013/10/20/book-review-love-and-math/#comment-34904 ), this great Trinity is then no more.
Sean,
what do you think of this proposal by Mukhanov
http://arxiv.org/pdf/1308.5410v1.pdf
I have never been too found of the idea that Dark Matter would be a WIMP, but has anyone found any relation to location’s in the cosmos that would produce the energies required to create a Higgs Boson and Dark Matter? Or, is the energy level needed to create a Higgs Boson too large to be found in nature?
I figure the Higgs Boson wouldn’t be able to be detected in such an experiment, because it would decay too quickly before it would be able to reach a detector. If the WIMP was a particle that decayed quickly, they would never find it with the current setup.
@John:
First, the Higgs boson DOES decay before it reaches the detector. It is detected via its decay products.
Second, the Higgs boson and dark matter have little, if anything, do do with each other.
Third, there was more than enough energy in the early universe.
“what do you think of this proposal by Mukhanov
http://arxiv.org/pdf/1308.5410v1.pdf”
Yes, Sean, give an executive summary and review. Note that Mukhanov recently won the Gruber Prize. (It was awarded while he was giving lectures at a summer school which I happened to be attending. No, correlation does not imply causation!)
http://gruber.yale.edu/cosmology/press/2013-gruber-cosmology-prize-press-release
Any paper which has as its only reference Landau and Lifshitz’s Classical Theory of Fields has to be worth reading, right?
@ Phillip
I know, it decay’s shortly after it is produce. So, the Higgs Boson would be detected from it’s decay products in the particle accelerator, but it would not detect the decay products in a mine on the other side of the world.
It would seem that if the Higgs Boson and Dark Matter have nothing to do with each other, then we would be all out of particles that could be the WIMP responsible for Dark Matter.
I have heard that the particle accelerators produce the energy of the early universe, and this is what raised the question if these same energies could be present today. In the history of particle physics it requires more energy to discover new particles. If we have already reached an energy level that surpasses what is found in nature, then it is hard to imagine there being some other particles responsible for Dark Matter. We should have already detected them in the accelerators. We should have accounted for all particles seen in nature already.
Then heavier particles would have a faster decay rate. It would seem like a particle heavy enough would decay too quickly to be found without a particle accelerator right next to the detector.
“It would seem that if the Higgs Boson and Dark Matter have nothing to do with each other, then we would be all out of particles that could be the WIMP responsible for Dark Matter.”
I am not aware of anyone else who holds this view.
“I have heard that the particle accelerators produce the energy of the early universe”
The key question is, how early?
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GeV WIMPs as the main source of dark matter was likely disproven before LUX announced their null results.
WIMPs with rest masses over ~16 keV have been ruled out by analyzing dark matter concentrations within galaxies.
See Table II and Figure II of the following paper.
http://arxiv.org/pdf/1311.0282v1.pdf
In order to fit all scales (and not clump up at the center of galaxies), the rest mass of dark matter needs to be on the order of 2-20 keV. CDM models significantly over-predict the amount of dark matter at the center of galaxies.
With that having been said, nobody has detected a 2 -20 keV dark matter particle. So, it is important to keep an open mind. But the astrophysical data certainly is pointing in the direction of a dark matter particle with rest mass in this range of values. The days of “GeV CDM” as the ruling dark matter theory are now over.