Future Promises and Prospects

7 Future Promises and Prospects

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, $γ$ -ray missions (GLAST [88 ]), 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 $m0$ and the gaugino mass $M1 ∕2$ as the coordinates. The two plots correspond to two illustrative values of tan $β$ . The solid dark green regions are already excluded. In the light green/yellow shaded area $0.025 ≤ Ωm ≤ 1$ , while in the blue shaded area $0.1 ≤ Ωm ≤ 0.3$ . 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 $γ$ -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.