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News & Public Affairs
University of Florida

Contact Information:

Writer: Aaron Hoover, (352) 392-0186, ahoover{at}ufl.edu

Source: Konstantin Matchev, (352) 514-8091, matchev{at}phys.ufl.edu

UF PHYSICIST: DARK MATTER, EXTRA DIMENSIONS TIED, POSSIBLY DETECTABLE

May 13, 2003

GAINESVILLE, Fla. -- A team of scientists that includes a University
of Florida physicist has suggested that two of the biggest mysteries
in particle physics and astrophysics -- the existence of extra time
and space dimensions and the composition of an invisible cosmic
substance called dark matter -- may be connected.

"For the most part, these two questions have been treated separately
in the past, and for the first time we're making a direct link," said
Konstantin Matchev, a UF assistant professor of physics. "We're 
suggesting that the dark matter may be due to extra dimensions."

If correct, the scientists' theory may lead to the discovery of the 
first concrete evidence of dark matter, an invisible substance that
may comprise as much as 30 percent of the universe. Dark matter has
never yet been directly or indirectly observed.

Matchev co-authored a paper on the subject that has been widely cited
by other scientists since appearing in the journal Physics Review
Letters in November. The other authors are Hsin-Chia Cheng and
Jonathan Feng, physicists at Harvard University and the University of
California at Irvine, respectively.

Scientists have long inferred dark matter is present based on a 
discrepancy between galaxies' rotational speed and the amount of
visible stars within them. In a nutshell, there are not enough stars
or visible objects to account for the speed, which means the galaxies
must also contain the invisible dark matter. Its composition is
unknown. 

Extra dimensions are predicted by the superstring theory, which
offers a unified description of all of the fundamental particles and
forces in nature, including gravity. While this widely accepted
theory predicts at least 10 dimensions, however, no one has ever
found more than one dimension in time and three in space.

According to one alternative theory, these additional dimensions
might be curled up into a ball so small -- significantly smaller than
atoms -- that they are difficult or impossible to observe. Matchev
said his team believes these dimensions may give rise to heavier
versions of known particles, the lightest of which could constitute
the elusive dark-matter particle. "This phenomenon of extra
dimensions provides a completely new dark-matter candidate," Matchev
said. "We named it Kaluza-Klein dark matter, after the two physicists
who first proposed theories with extra dimensions in the early
1920s."

Most important is that Kaluza-Klein dark matter may be detected using
a variety of current and future experiments, Matchev said. In
addition to dedicated underground searches designed specifically to
look for dark-matter particles, Kaluza-Klein particles may give
distinct, albeit indirect, signals in numerous other experiments, he
said. 

For example, an ongoing experiment on the South Pole designed to
detect elementary particles called neutrinos -- as well as an
antimatter detector set to be placed aboard the International Space
Station -- could be used to find these heavier particles.

The South Pole device, known as the Antarctic Muon Neutrino Detector 
Array, or AMANDA, is designed to detect particles with no electrical 
charge and no mass created in massive cosmic events such as
supernovas.  But this "neutrino telescope" also may pick up telltale
high-energy neutrinos necessarily created when dark-matter particles
collide where they are most concentrated, at the gravitational
centers of stars and planets. The detection of these types of
neutrinos from these areas would provide indirect evidence of dark
matter, Matchev said. 

"Most of the stuff produced by dark-matter particle collisions is 
probably absorbed in the dense cores of the sun or the Earth, but the 
neutrinos, being so weakly interacting, escape and may reach our 
detectors," Matchev said. "So what we're looking for are unusual
sources of neutrinos near gravitational centers."

Matchev said scientists also have a separate shot at detecting dark 
matter in a future antimatter detector, the Alpha Magnetic
Spectrometer, slated to reach the International Space Station in
2005. The detector may pick up positrons, the antiparticles of
electrons, similarly created when the dark-matter particles collide.

"If we see more positrons than we expect, then we know there is 
something going on," Matchev said. "What is more, the positron signal
is rather unique for Kaluza-Klein dark matter and may thus provide
the first evidence of extra dimensions."

Yet another experimental apparatus, the Gamma Ray Large Area Space 
Telescope, is slated for satellite launch in 2006. This telescope
could discover very high-energy photons and help nail down the
identity of dark matter, Matchev said.

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