**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*^{-1}*Mpc*, and the power spectrum of
fluctuations at
*z* ~ 10^{3} on scales
100 - 1000 *h*^{-1}*Mpc*, 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*^{-1}*Mpc* scales.
COBE data put limits on scales ~ 1000 *h*^{-1}*Mpc*.
Accumulating ground-based and balloon data of CMB fluctuations
with sub-degree resolution start providing constraints on
scales ~ 100 *h*^{-1}*Mpc*.

*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:
_{m}*h*_{65} *n*^{2} = 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].