postscript
Abstract...
Abstract...
2 Model...
There exist several mechanisms which produces anisotropies on the CMB: the primary anisotropies which take place at the last scattering epoch and the secondary anisotropies such as the Sunyaev--Zel'dovich effect which occurs while the CMB photons are travelling through the universe. We will concentrate here on a particular secondary anisotropy first discussed by Rees & Sciama (1968). As pointed out by these authors, there is a gravitational effect on the CMB photons while they are crossing evolving cosmic structures such as a collapsing cluster of galaxies or expanding voids. Indeed photons climb out of a slightly different potential well than the one into which they entered. This effect is usually referred as the Rees--Sciama effect.
Early approaches to this problem were based on the ``Swiss Cheese'' model (Rees & Sciama (1968), Dyer (1976), Kaiser (1982), Nottale (1982), Nottale (1984)), whereas more recent attempts have used the continuous Tolman--Bondi solution (Panek (1992), Sáez et al. (1993)). Our aim is to present here an improved model which, for the first time, treats such a problem exactly (see section 2).
In section 3 we apply our model to a rich galaxy cluster at a
redshift 
. We investigate the properties of the collapsing cluster and
verify that its density-profile is of a realistic shape. We then give, in
section 4, an upper limit for the temperature decrement that such an
evolving cosmic structure could imprint on the CMB. Our result is compared to
previous works.
Section 5 deals with distant clusters (
) since it is
reasonable to assume that, at such an epoch, those objects were in a stage of
formation and that our spherical collapse model would be suitable. The focus is
put on the gravitational lensing phenomenon and how this would distort the
observed CMB power spectrum.
We finish in section 6 by a short conclusion and discuss the applicability of our work to model the microwave decrement observed towards the, possibly lensed, quasar pair PC1643+4631 A&B.
The methods and results introduced in this poster are discussed in further details in forthcoming papers (Lasenby et al. (1997), Dabrowski et al. (1997)).