links for 2009-07-18

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Scientists and Kool-Aid § Unqualified Offerings "In my department weâll often produce documents that have lots of buzzwords, but nobody really takes it seriously. You can always get appreciative chuckles in a department meeting if you poke fun at your own handiwork. Higher on the food chain,…
Physics Buzz: Watch this! "Forget the cheesy narrator and hokey graphics. Wobble the camera like you're Michel Gondry filming Eternal Sunshine. Ditch the pseudo-techno soundtrack that makes the kids shake their heads at you for trying to be hip, and go for something understated. Then you might…
The Virtuosi: Would a laser gun recoil? "Let's motivate our question a little bit. I've wondered about this question since I saw star wars. Though I'm no firearms expert, the recoil in guns must come from conservation of momentum principles. Momentum is conserved in a system. The gun starts with…
Physics Buzz: When chemistry dunces bake "Shirley Corriher, a former research biochemist at Vanderbilt University, got her start in the kitchen burning scrambled eggs beyond all recognition. Later, when she ruined recipes while taking a cooking class, she impressed her teacher by being able to…

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....