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Cosmic Antimatter Excess Confirmed
sciencehabit writes "In 2008, the Italian satellite PAMELA picked up an unusual signal: a spike in antimatter particles whizzing through space. The discovery, controversial at the time, hinted that physicists might be coming close to detecting dark matter, an enigmatic substance thought to account for 85% of the matter in the universe. Now, new data from NASA's Fermi Gamma-ray Space Telescope confirm the spike (abstract)."
I'm confused, is this about antimatter or dark matter?
...zipping by to see if we've eliminated ourselves yet.
Orwell: "In a Time of Universal Deceit, telling the Truth is a Revolutionary Act"
What I am afraid of, if anyone ever cared... ;)
What I am afraid of is that some people will use this as evidence of otherworldly forces (any Slashdot reader), supreme beings (any Slashdot reader), Batman (a DC comic), demons (a variety of delusions), Thor (The Norse God), Bogeyman (an American tell tale), Akhenaten's Ra (Akhenaten the monotheistic precursor to the Abrahamitic monotheistic "Yahweh"), Santa Claus (The Coca Cola version of a Norse tradtion), Green Lantern (a DC superhero), Sherlock Holmes (a Doyle detective), King Kong (a Hollywood movie), or whatever has sprung out of man's mind.
Dark Matter. Ok, calm down, we won't bite.
It doesn't matter
Ask me about repetitive DNA
goatse alert
In my opinion and in contrary to what the original posting suggests, anti-matter should not be viewed as particularly "dark".
E.g., anti-Hydrogen, consisting of an anti-proton and a positron, will readily absorb a quantum of energy (a photon, which happens to be one of the particles that are their own anti-particles) and re-emit a photon again, just like "plain old" hydrogen. Thus, a cloud of anti-hydrogen should be observable as easily (or difficultly) as a cloud of hydrogen, assuming their masses, their viewing distances and all other parameters like temperature, density etc. being equal.
So there should be no difference in observability here, due to the fact that photons are citizens of both realms, of "nornal" matter as well as of anti-matter, and will interact with mass particles of both realms in the same way.
Obviously, "dark matter" looks like a very different beast...
Until My Kingdom cometh.
Ah, so when he wrote "supreme beings (any Slashdot reader)", you must be the reader he had in mind.
Sheesh, evil *and* a jerk. -- Jade
What is mind?
No matter.
What is matter?
Never mind.
Antimatter galaxies (or at least clumps) seem like they could also plausibly explain this. That's not an outright endorsement of the theory but I can't help but think that they've got insufficient evidence to show causal link.
They're saying:
1. lots of energy released (presumably when dark matter interacts)
2. anti-matter is created
An equally plausible interpretation is:
1. the anti-matter already exists
2. the interactions with small amounts of matter cause the energy release
I may have missed it, but I don't see anything to rule that possibility out. The primary objection to the anti-matter galaxy theory is that we don't see a lot of annihilation events; This could just as easily be those exact events.
The neutralino would be a composite particle, composed of the super-partners of the guage bosons and the higgs - that is wino (w partner), higgsino (higgs parnter), bino (partner of the weak hypercharge). Since the symmetry is broken, we don't see the original super-partners, only their super-imposed forms with the same mass eigenstate.
When particles annihilate, they produce a set of particles that have a quantum number of 0. Any particles with the same mass-energy as the original colliding pair of particle and anti-particle can be produced. If mass energies are low, this means that the result will be mostly photons, because photons have no mass, and are only energy. That is, they have a low total mass energy. But any particles can be produced, so long as the result totals to 0, and has the same mass energy.
Neutralinos, as you would guess, from the term WIMP, are weakly interacting, and massive. That means that when a neutralino annihilates another, particles with greater mass energy can be produced.
In a 1994 paper Drees et al calculated neutralino decay into gluons. One of the co-authors here Kamionkowski went on to publish more on dark matter and neutralinos. There have been other papers on other possible decay products from neutralino annihilation, because, of course, if annihilation produces unstable particles, or anti-particle pairs, it can keep going until it reaches an end state of stable products. However, not all anti-particle pairs produce annihilate, and if the products are stable, they go bouncing on their merry way.
This means that anti-protons and positrons above the background, and at certain energy levels could be the signature of neutralino dark matter.
Or to roll things back: one of the few ways, other than gravity, we can detect WIMPS is from their annihilations. To determine if, and if so, what, WIMPs are composed of, we have to look at the decay products of those events. The Pamela data shows that there is an excess of positrons, however, it does not show that this excess is from WIMP annihilation. The search for this spectrum is important for both large and small reasons: large because cosmology evolves based on mass, and small because neutralinos, if detected, tell us about the final broken super-symmetrical extensions to the Standard Model, and in turn tell us about the super-partners, and, in turn, about the partners. For example, we have not seen a higgs boson, but a neutralino is an eigenstate of a higgsino fermion, which implies a higgs boson to be partnered with. Back in the 1990's Drees et al published
Fugue for Aaron Swartz
You feel that there isn't a sufficient amount of irrationality out there to generate wars now, but after dark matter is discovered, there will be a big increase?
"Who is the Journal of Quantum Physics going to believe?" --Stephen Hawking
If the article would report everything, it would be talking about momentum, and virtual particles too.
It would not report on virtual particles because the annihilation takes place in the galactic core where the densities of DM are highest and virtual particles can only exist for the tiniest fractions of an instant not the ~50k years needed to make it from the core.
The question you should be asking is where are all the anti-protons? Since DM particles generally need to have masses roughly ~100 or more times the mass of the proton their annihilations should be capable of producing all stable anti-particles below this. Hence most models predict an excess of anti-protons as well as positrons but no satellite has seen any evidence of this. So if this positron excess is due to DM (and that is a BIG if!) we may have to start looking at some of the more exotic DM models (e.g. Arkani-Hamed et al. Phys Rev D (2009) vol. 79 (1) pp. 015014) which some of us are already looking for with the LHC.