5.3. Present Structure versus Fluctuations in the CMB
This method is using independent constraints on the power spectrum of today's fluctuations on scales ~ 100 h-1Mpc, and the power spectrum of fluctuations at z ~ 103 on scales 100 - 1000 h-1Mpc, assuming gravitational growth.
New Developments: Peculiar velocity data enable constraints on m independent of biasing. Future extended redshift surveys (2DF, SDSS) will provide constraints on > 100 h-1Mpc scales. COBE data put limits on scales ~ 1000 h-1Mpc. Accumulating ground-based and balloon data of CMB fluctuations with sub-degree resolution start providing constraints on scales ~ 100 h-1Mpc.
Pro: With peculiar velocity data this method compares measures of dynamical fluctuation fields independent of galaxy biasing.
Con: As long as the scales explored by today's structure and the CMB fluctuations do not overlap, the constraint on m depends on n. A hot dark matter component would alter the result via a different fluctuation growth rate, and confuse the constraints. If today's power spectrum is extracted from a galaxy redshift survey then the method depends on galaxy biasing on large scales.
Current Results: Using COBE and Mark III velocities, and considering the family of Inflation-motivated CDM models with a possible cosmological constant such that m + = 1 and a possible tilt in the initial power spectrum, a likelihood analysis yields: mh65 n2 = 0.7 ± 0.1 . The best fit for CDM is thus obtained with a slight deviation from the ``standard'' CDM model, of either n ~ 0.8 - 0.9, m ~ 0.7, or ~ 0.2. The indicated height of the first acoustic peak of the CMB allows only a slight tilt, n ~ 0.9, and a high baryon content, b ~ 0.1 .