Table 1 shows the acceptable range of values for the key parameters that came out of those fits. In the table the matter density, , includes both baryonic matter and dark matter, and moreover the dark matter can be classed either as “hot” or “cold” depending on whether it was relativistic or not in the early Universe. The total dark matter density is , and . Of particular note for this review were that the cold dark matter density is non-zero and that the baryonic density has a range that just accomodates the constraints from BBN  at its lowest end, but with significantly better fits for higher values. The hot dark matter density can only be a minor component.
Very recently there have been significant new CMB data released from BOOMERANG , MAXIMA , DASI , and CBI . These data have given better definition to the second and third peaks in the CMB power spectrum. Wang, Tegmark and Zaldarriaga  subsequently repeated the above analysis using a combination of these and previously available CMB data.
The two left-hand plots in the top row in Figure 1 are the most relevant for the dark matter. We see that the dark matter density is again non-zero, with a similar range of values as before, and that the fraction of dark matter as “hot dark matter” is less than 35%, assuming no constraints on the hubble parameter, . The allowable fraction of hot dark matter drops to only 20% if the preferred hubble parameter value is imposed. The right-hand column in Table 1 lists the quoted 95% confidence limits for comparison with the earlier analysis. The most striking difference is in the baryon density. While previously the allowable range of was only just compatible with the upper limit derived from BBN , it now comfortably embraces it. This is illustrated in the left-hand panel in Figure 2, which shows the combined constraints on the baryonic matter and dark matter densities. The white central region is the allowed parameter space when all constraints are applied, except for BBN of course. Relaxing the constraints by not using the PSCz data enlarges the allowed region to include the cyan coloured area. If, in addition, no assumptions are made about the value of the Hubble constant, then the green area also becomes allowed. If all constraints are accepted then Figure 2 implies there is between 4.5 and 9 times as much dark matter in the Universe as there is baryonic matter.
Constraints on cosmological models can also be derived from the observations of high red-shift Type 1a supernovae . When combined with data from the CMB anisotropies, these limits give reasonable agreement with those cited earlier in Table 1. A recent result from de Bernardis et al.  is shown in the right-hand panel in Figure 2. This time what is shown are the joint constraints on and . The solid curves are the 1 to 3 combined likelihood contours and these can be compared with the values in the table. A somewhat weaker constraint on the Hubble constant was used.
Hence, from the above, there does indeed seem to be a cosmological model that can simultaneously satisfy all the observational evidence used. The ranges of values for the key parameters relevant to dark matter searches have been summarized in Table 1. Rotation curves of galaxies can also be explained with this type of cosmological model. Numerous N-body simulations have been performed to verify whether structure formation occurs properly in a number of different types of models. Gawiser and Silk  reviewed the situation with regard to large-scale structure. Simulations of gravitational collapse on the scale of galaxies have resulted in universal rotation curves that match reasonably well those observed in a wide range of galaxies [93, 94].
From Table 1 the main features of the emerging standard cosmology from the point of view of dark matter are:
The origin of remains a topic of current debate, with a great deal of interest in quintessence [29, 9].
© Max Planck Society and the author(s)