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In the description of the evolution of density inhomogeneities, one
often make the simplifying assumption that the initial powerspectrum
has the simple powerlaw expression
. Although the
scalefree Zeldovich spectrum, , is expected on the
grounds of the classical inflationary scenario, nevertheless
distortions of its shape should arise during the subsequent phases of
cosmic expansion, and characteristic scales are imprinted on the form
of at the onset of the structure formation. Since the amount
of such distortions and the scales at which they occur are strictly
related to the nature of the fluctuations and to the matter content of
the Universe, their knowledge becomes of crucial relevance in order to
fix the initial conditions for the galaxy formation process.
Theoretical models for the determination of the powerspectrum, which is
responsible for structure formation, starts from the assumption of a
primordial at a sufficiently high redshift,
[
is the redshift of the epoch
of matterradiation equality]. The usual choice corresponds to
the HarrisonZeldovich spectrum. Due to the evolution of density
perturbations, the slope of the powerspectrum is left unchanged at
wavelengths
, that exceed the horizon
size at . On the contrary, the shape of the spectrum at
crucially depends on the nature of the matter which
dominates the expansion. In order to account for these effects, the
postrecombination spectrum is usually written as

(21) 
where the transfer function conveys all the informations
about the prerecombination evolution and the nature of the matter content.
Subsections
Next: The evolution of baryonic
Up: THE LARGESCALE STRUCTURE OF
Previous: The Zeldovich approximation
Waleska Aldana Segura
20010116