UCI: Link between excess positrons and dark matter doubted

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UCI: Link between excess positrons and dark matter doubted

Post by bystander » Fri Apr 16, 2010 3:06 pm

UCI astrophysicists cast doubt on link between excess positrons and dark matter
UC Irvine - 15 April 2010
Astrophysicists are looking everywhere – inside the Large Hadron Collider, in deep mines and far out into space – for evidence of dark matter, which makes up about 25 percent of the energy density of the universe.

Despite the recent tantalizing observation of excess high-energy positrons – thought to be due to dark matter – UC Irvine researchers say we’re not quite there yet.

Models predict that when dark-matter particles collide, they’ll annihilate some of the time into electrons and positrons, said Manoj Kaplinghat, physics & astronomy associate professor. Scientists working on a satellite experiment called PAMELA recently identified a large excess of positrons, causing a flurry of excitement about having detected dark matter.

Kaplinghat – working with Jonathan Feng, UCI physics & astronomy professor, and Hai-Bo Yu, postdoctoral researcher – evaluated the dark-matter explanation for the PAMELA finding. “What we concluded is that the detection of so many positrons makes it unlikely they’re all from dark matter,” Kaplinghat said.

The UCI study sharpens predictions of what scientists can expect to detect from the annihilation of dark-matter particles in our galaxy. While it shows that currently popular models cannot account for the excess positrons observed, it leaves open the possibility that discovery of dark-matter evidence could be right around the corner, perhaps within reach of current and planned experiments.

The UCI team’s study was published April 15 in Physical Review Letters and is suggested reading by the editor.
Halo-Shape and Relic-Density Exclusions of Sommerfeld-Enhanced Dark Matter Explanations of Cosmic Ray Excesses