New Class Of Superweak Particles May Reveal Secrets Of Hidden Mass In Universe. - but perfectly viable, alternative for dark matter."

Source: University Of California - Irvine
Date:
2003-07-09


New Class Of Superweak Particles May Reveal Secrets Of Hidden Mass In
Universe
Irvine, Calif., July 8, 2003 -- A UC Irvine study has revealed a new class
of cosmic particles that may shed light on the composition of dark matter in
the universe.

These particles, called superweakly interacting massive particles, or
superWIMPs, may constitute the invisible matter that makes up as much as
one-quarter of the universe's mass.

UCI physicists Jonathan Feng, Arvind Rajaraman and Fumihiro Takayama report
that these new superWIMPs have radically different properties from weakly
interacting massive particles (WIMPs), which many researchers have long
looked to as the leading dark matter candidate. The study was posted July 3
on the online version of Physical Review Letters (http://prl.aps.org/).

The identity of dark matter is one of the most puzzling problems for those
who study the nature of our cosmos. While as much as a quarter of the
universe is made of this invisible mass, which plays a vital role in the
structure of the universe, almost nothing is known about its composition. It
is believed to be the celestial glue that holds galaxies together in their
distinctive spiral shapes.

To identify this elusive dark matter, many astrophysical researchers have
turned to WIMPs. These particles emit no light and are very difficult to
detect. However, as their name suggests, they do have weak-force
interactions with other particles, and they are expected to leave visible
traces in experiments. Currently, research groups throughout the world are
searching for WIMPs, so far without success. But in studying theories that
predict WIMP dark matter, Feng and his colleagues found that in many of
these theories WIMPs do not live forever. According to Feng, many theorists
have assumed WIMPs to be the lightest particles and thus the most stable.
"But we've found that WIMPs are often not stable at all, because they can
decay into lighter particles," Feng said, "and, all of a sudden, the WIMPs
disappear."

These new, lighter particles are superWIMPs. Like their progenitors, they
emit no light and have both mass and gravitational force. But they are
incapable of the type of weak-force interactions that WIMPs have; they can
only interact gravitationally. Since the gravitational force is not as
strong as the weak force, these interactions are, as Feng calls them,
"superweak." In turn, these particles will rarely, if ever, collide with
other particles.

And, unlike WIMPs, superWIMPs are incapable of decaying into other
particles. "They are absolutely stable," Feng said. "And because of this,
they are a completely different, but perfectly viable, alternative for dark
matter."

Like WIMPs, superWIMPs only exist theoretically. In fact, because superWIMPs
do not have weak-force interactions, they are predicted to be impossible to
detect by conventional experimental methods. But Feng and his colleagues
point to some alternative tests to prove their existence. They found that
observations of old stars and the cosmic microwave background of the
universe can reveal clues for superWIMPs.

"One place to look for evidence is in the cosmic microwave background, which
in essence is the afterglow of the Big Bang," Feng said. "This background is
very uniform. But according to our theory, WIMP decay would set loose a zoo
of particles that would create deviations in this background. If such
deviations are found, they would provide a particle fingerprint for the
existence of superWIMP dark matter."

Feng and his collaborators are currently investigating hints for superWIMPs
in present data and are considering further studies that might provide
evidence for the existence of superWIMP dark matter.


The research was funded by UC Irvine and a CAREER Award from the National
Science Foundation.

Editor's Note: The original news release can be found here.


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