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 [41]. 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 [59].