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"Uncertain Principles" features the miscellaneous ramblings of a physicist at a small liberal arts college. Physics, politics, pop culture, and occasional conversations with his dog.

Chad Orzel "Prof. Orzel gives the impression of an everyday guy who just happens to have a vast but hidden knowledge of physics." (anonymous student evaluation comment)

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« Belated Baby Blogging 071709 | Main | links for 2009-07-19 »

links for 2009-07-18

Category: Links Dump
Posted on: July 18, 2009 5:00 AM, by Chad Orzel

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The two dark matter papers you link are, in fact, asking completely different questions. Bergström et al are looking at the spectrum of high-energy positrons and electrons (in the range of 100s of GeV), where there seem to be more positrons than expected. This might be due to dark matter annihilating or decaying (with a mass scale of ~ 1 TeV), or could be from pulsars or some other standard astrophysical way of producing cosmic rays that just hasn't been understood well enough yet. In any case, these high-energy positrons are produced somewhere relatively nearby and are being detected directly in satellite and balloon experiments.

Lingenfelter et al, on the other hand, are interested in the bright 511 keV radiation coming from the center of the galaxy (as seen by the INTEGRAL experiment). Because it's 511 keV, the natural assumption is that it's from slow-moving electrons and positrons annihilating to two photons. So while positrons are involved, they are in a completely different energy range than the ones being studied in the other paper. Dark matter explanations of this might involve light (MeV-ish) dark matter, or heavier dark matter with an excited state that is split from the ground state by a similar small energy.

Both are interesting, but they're far from being the same question....

Posted by: onymous | July 18, 2009 12:14 PM

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