Saturday, April 20, 2013

A Heavy Dark Matter Particle is an Oxymoron

So, there's been a lot of news recently about possible evidence for a dark matter particle. But this is probably just media hype. The science media (such as New Scientist) has been going full throttle since the Higgs discovery last year, and now they don't know what to do with themselves, so they jumps on any news, regardless of its quality.
And that's the case with the recent hype about finding evidence for a 8.6 GeV dark matter particle using an underground detector in Minnesota, USA.
If you're not familiar with the story, check out one of the following articles before continuing:

New Scientist: Tentative dark matter hits fit with shadow dark sector
New Scientist: Going Underground in Search of Dark Matter Strikes

The actual data results can be found here.

A realistic assessment can be found at the Résonaances blog

Résonaances: More mess with dark matter detection

At the Résonaances blog, I posted a general criticism I have with the idea of a heavy dark matter particle, i.e. a WIMP  (Weakly Interacting Mass Particle.) The idea is that such a particle is really massive (large rest mass) but that it does not interact via the strong nuclear or electro-magnetic force.

The problem with the idea of a WIMP is that it goes completely against the trends in the experimental data we have for Fermi particles.
The heavier a particle is, then the more unstable or the more reactive it is. For example, of the 1st generation fermions (i.e. up/down quark, electron, and e-neutrino), the quarks are heavier than the electron, and the electron is heavier than the e-neutrino. The number of forces available to the particles decreases likewise (the quark can interact via all four of the forces, the electron can interact via 3 of the four forces, and the e-neutrino can interact via only 2 of four forces.)
The existence of a WIMP that can interact via only the weak nuclear and the gravitation forces completely goes against the trend in the Standard model (that particles develop mass by their interactions.)
There is a similar trend within families of fermions. For example, the bottom quark is heavier than the strange quark, which is also heavier than the down quark. The bottom quark has a mass of 4.2 GeV, and the lifetime of particles containing the bottom quark is much shorter than the lifetime of particles that contain the strange or especially the down quark. In other words, the more rest mass, the shorter the lifetime.

In other words, a heavy dark matter particle is an oxymoron   (or there is some unknown dark force between these particle that somehow is not available to the other particles. Of course, we should be skeptical of the idea of a new force of nature that we develop only for specific problems without looking at full implication of a new force of nature.)

The other problem with a WIMP at 8.6 GeV is that we would have already found evidence of such a particle at CERN, FERMI lab or the SLAC. We would have found evidence for these particles (and their anti-particles) because the energy of these accelerators is well beyond the ~20 GeV required to make such a pair of particles.

I don't claim to be able to explain the CDMS results, but what I'm saying here is that we shouldn't jump to conclusions based off of three data points in a particle detector under the ground measuring recoil energies of particles in the keV range. The jump to a 8.6 GeV particle, and then the further jump to a 8.6 GeV dark matter particle is a little bit of a stretch of the imagination. It just seems like there are a number of other explanations for these 3 signals. What is the chance that CERN, FERMI lab and SLAC failed to find a 8.6 GeV WIMP, but some underground detector found these particles by looking at recoil velocities in the keV range?  I remain skeptical of this claim, and I hope you do too.


May 27, 2013: As an aside, most models of the universe are suggesting that the mass of particles that best describe the formation of structures (i.e. galaxies) in the universe is around 0.5-3 keV.

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