Neutrino
signal rates can be enhanced by the trapping of WIMPs in massive
bodies, such as the Sun, Earth, or Galactic centre; the WIMP
density builds up until the annihilation rate equals the capture
rate. For the Sun this equilibrium situation has already been
reached. For Earth this may not yet be the case and annihilation
fluxes may be only 10% of that expected in equilibrum. The
capture rate will depend on the scattering rates for WIMPs on the
various nuclear species in the body and the energy transfer per
scatter. The scattering rate on a particular species will depend
on the abundance of the species and the cross-section. The
scattering cross-sections are usually calculated [49] within MSSM constraints, abundances depend on which body the
WIMPs are being trapped in, and energy transfer per collision
normally assumes elastic scattering with the WIMPs starting out
with a typical virial speed of
for particles bound to the Galaxy. Once capture rates, and hence
annihilation rates, have been derived, the neutrino flux is
calculated from the branching ratios for WIMP annihilations going
into neutrinos. Neutrino products are typically in the GeV energy
range and are hence accessible to existing solar neutrino
experiments. However, for contained events (ones in which the
muons produced by the neutrinos are stopped in the detector) the
predicted rates
are a few events for kiloton of detector per year, while
traversing signals (muons produced in surrounding rocks and
passing through the detector) occur at a rate
.
A
is the detector area in
. Results from this type of experiment first appeared in the
mid-1980s [46].
Early studies of
-ray
signatures from WIMP annihilation predicted both continuum
emission from
products, and line features from
and direct WIMP annihilation into photons
[129,
130,
49
]. Continuum emission fluxes were predicted to be about two
orders of magnitude lower than the diffuse galactic background.
However, some enhancement would be expected in the direction of
the galactic centre. Line emission features should be much easier
to see above the background as long as good energy (
%) is available.
Antiproton
fluxes from WIMP annihilation were expected to produce
measurable enhancements above typical background fluxes in the
low-energy antiproton spectrum (), which would be accessible to space instruments such as
AMS [4]. However, it is now thought that there will be additional
background fluxes that will make this type of measurement
difficult.
Positron
features around 50-100 GeV are expected from neutralino
annihilations. These may be visible as bumps in the otherwise
smooth background spectrum due to cosmic-ray interactions with
interstellar gas. Signals are expected to be much below the
background levels, and long-duration space missions will be
needed to collect sufficient statistics to observe the
positrons [49].
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Experimental Searches for Dark Matter
Timothy J. Sumner http://www.livingreviews.org/lrr-2002-4 © Max-Planck-Gesellschaft. ISSN 1433-8351 Problems/Comments to livrev@aei-potsdam.mpg.de |