
Given the level of current activity it is inevitable that over
the next several years there will be substantial advances in
``the dark matter problem.'' The main issues will be:
- Refinement/Revision of the Standard Cosmological Model
using:
- New observational data on CMB anisotropies, particularly
the second peak. Definitive data should come from the ESA
PLANCK mission due for launch in 2007. Balloon-borne
instruments may also be useful.
- New observational data on large-scale structure from
galaxy redshift surveys.
- Improved statistics on high-redshift Type Ia supernova.
This is needed to provide proper confirmation of their
properties and their use as standard candles and also to
define the distribution more clearly.
- Further work on non-standard BBN models, such as those
invoking degenerate neutrino species.
- Continued theoretical modelling of the CMB anisotropies
using cosmological models. Although this appears to have been
developed to a fine art, there must be avenues for new
development.
- Investigation of alternative types of dark matter, such
as ``warm dark matter.'' Further experimental data on the
neutrino masses would be relevant here as well, although the
recent evidence for neutrino mixing from SNO suggests that
the neutrino masses are unlikely to be cosmologically
significant [5].
- Refinement of Galaxy Formation and Structure Models using:
- Continued high-resolution
N
-body simulations including more refined feedback on baryonic
condensation, star formation, and massive black-hole
formation.
- High-resolution rotation curve measurements. These will
help to establish the central density distributions and will
also look for modulations at larger radii to assess dark
matter infall models.
- High-resolution
N
-body simulations to establish CDM dynamics and structure
within galaxy halos.
- Continued observational searches for cold baryonic dark
matter, using microlensing or infra-red, sub-millimeter
observations of small clouds.
- Experimental Searches for Neutralinos, including:
- Improved versions of CDMS, CCREST, and UKDMC experiments
in the next two years, which will extend significantly below
the DAMA region and resolve whether neutralinos have already
been observed or not.
- Several other experiments, such as GENIUS [76], that may also come online in the next several years. In
fact, within about 6 years it is just possible that the whole
of the parameter space in figure
6
will have been explored.
- A number of indirect search experiments may produce
useful complementary data, such as neutrino telescopes,
-ray missions (GLAST [89]), or particle experiments (AMS).
- Detectors with directional response will have been
developed at the prototype level, ready to become neutralino
``telescopes'' should the need arise.
- Supersymmetry and Supergravity will have independent input
from:
- The Large Hadron Collider, which will begin operation in
5-6 years time. Within a few years of data taking it should
start to constrain much of the MSSM and SUGRA parameter
space.
- Continued exploration of MSSM and SUGRA models to refine
calculations of scattering cross-sections.
Figure 17:
Expected progress in covering MSSM parameter space from both
indirect and direct search techniques over the next several
years [49
].
Of course, the most satisfying scientific output would be the
discovery of the neutralino as the dominant dark matter component
of the Milky Way. The prospects for this are very good.
Figure
17
shows two panels taken from [49
] in which the likely search areas to be completed by 2006 are
delineated. The parameter space chosen for these plots has the
universal scalar mass
and the gaugino mass
as the coordinates. The two plots correspond to two illustrative
values of tan
. The solid dark green regions are already excluded. In the light
green/yellow shaded area
, while in the blue shaded area
. The curves then show which regions of parameter space are
likely to be addressed over the coming years. For each curve the
forth-coming experiments will search the region between the curve
and the dark green area. The red curve corresponds to the direct
search techniques such as the next generation of CDMS, CCREST and
UKDMC Xenon experiments. This curve should be reached in 2-3
years time. Following that, there are already larger, better
experiments being planned that could push further still [133]. The other curves shown correspond to various indirect search
techniques, including
-rays, neutrinos, and positrons. Feng et al. [49] describe the situation in great detail. The complementarity of
the various techniques is apparent and multiple detections would
provide a powerful diagnostic of SUSY parameters.
The scientific impact of a positive neutralino detection would
extend not only to cosmology and astrophysics in almost every
aspect, but would also be of the utmost importance to
supersymmetry and fundamental physics. If, in addition to the
neutralino, the axion is also implicated, then we will have a
double bonanza, which also will verify the adopted solution to CP
violation. Seldom has there been a problem that impinges on so
many fundamentally important issues and this justifies the
current level of activity on all fronts. The next several years
promise to be very interesting.

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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
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