### 4. LARGE-SCALE FLUCTUATIONS; COSMIC FLOWS

These methods use the mean motions induced by the large-scale
mass distributions on scales of several megaparsecs and above.
They are based on GI in the linear regime
and approximate extensions into the mildly-nonlinear regime.
The different matter contributions to
_{m} are relevant,
such as ``cold'' and ``hot'' dark matter (see
[33] for a review),
but the cosmological constant is not involved.
The statistical nature of the initial fluctuations has to be specified in
some cases; it is commonly assumed to be a *Gaussian* random field.
The initial fluctuation power spectrum is characterized by the power
index *n*
on large scales, by a specific shape (*e.g.*, as predicted by
CDM theory), and by its amplitude, *e.g.*, via
_{8},
the *rms *fluctuation in top-hat spheres of radius
8 *h*^{-1}*Mpc*.
Galaxy *biasing* is expected to enter in a simpler manner on these larger
scales, but is still an important unknown. In the common simplified
treatments it is modeled as a linear biasing relation between the density
fluctuations of galaxies and mass,
_{g} = *b*
, with different
biasing parameters for different galaxy types: *b*_{iras},
*b*_{opt}, etc.
However, non-trivial properties of the biasing scheme may be important.