Dark Matter meeting

Latest science shows few answers on dark matter, but scientists hope for more from Large Hadron Collider

May symposium of the Space Telescope Science Institute, Baltimore, May 2–5, 2011
Dark Matter

No gamma-ray signs of dark matter
The Fermi Gamma-ray Space Telescope has failed to find definitive evidence of dark matter after more than two years of searching, Robert Johnson of the University of California, Santa Cruz reported May 4. The telescope hunts for dark matter indirectly, by looking for gamma-rays produced when the proposed particles would collide and annihilate.  At the Milky Way’s center, where dark matter is predicted to be densest, Fermi found no gamma-ray excess that could clearly be attributed to the material. Among 10 dwarf galaxies, which have a higher ratio of dark to ordinary matter than larger galaxies, Fermi found no gamma rays at all. The non-detection hints that if dark matter particles called WIMPs exist, they weigh more than about 33 times the proton’s mass. —Ron Cowen


Cosmic theory hard to improve
The leading theory of the evolution of the universe — a recipe that includes dark matter, Einstein’s theory of gravity and a constant density of dark energy — is still the best for describing the large-scale arrangement of galaxies as well as the detailed map of the early universe. That’s the conclusion of Constantinos Skordis of the University of Nottingham in England, who found major problems with four alternative ideas that replace dark matter with a modified form of gravity.  But the leading theory still has difficulties explaining  some properties of individual galaxies and the number of the lowest-mass galaxies, he and others noted on May 4. —Ron Cowen

Dark side of supersymmetry
The Large Hadron Collider, the powerful particle accelerator near Geneva, is likely to be able to confirm or negate a particle theory called supersymmetry within a year, Albert De Roeck of CERN and Antwerp University in Belgium said May 5. According to supersymmetry, every known elementary particle has a heavier partner with a different intrinsic spin. If correct, the theory would not only unify the four known forces of nature but could shed light on dark matter. A leading dark-matter candidate, known as the WIMP, is believed to be the lightest stable supersymmetric particle. WIMPs would make their presence known in the form of missing energy in particle collisions, but could take longer to find if they have a relatively low mass, as some recent studies suggest, says De Roeck. —Ron Cowen

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