News in Brief: Dark Matter meeting
May symposium of the Space Telescope Science Institute,
Baltimore, May 25, 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 Ways 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 protons mass.
Ron Cowen
Cosmic theory hard to improve
The leading theory of the evolution of the universe a recipe that
includes dark matter, Einsteins 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. Thats 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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