Physics
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........12s&link_type=abstract
Thesis (PH.D.)--MASSACHUSETTS INSTITUTE OF TECHNOLOGY, 1995.Source: Dissertation Abstracts International, Volume: 56-06, Secti
Physics
1
Cosmic Microwave Background
Scientific paper
I investigate the theoretical aspects of light propagation through the universe in the framework of a weakly perturbed Robertson-Walker model. Assuming that the metric perturbations are small, which is a valid approximation almost everywhere in our universe, I derive the general equations of light propagation using the geodesic equations in a perturbed space-time. These equations are used to study the temperature and spatial distribution of light, with the goal of comparing the theoretical predictions to the actual observations. The first part of the thesis is dedicated to the study of temperature distribution in the cosmic microwave background (CMB). I start with primary contributions using the linear theory analysis, which is an excellent approximation if the anisotropies were generated when the universe recombined at a redshift around 1100. I present a treatment of perturbations based on a tight-coupling approximation, which simplifies the equations significantly and enables one to identify the physical processes and parameters, while at the same time preserving an accuracy of 10-20% when compared to the exact results. Using this model I identify 6 physical parameters that can be determined from the measurements of CMB anisotropies. Next I analyze the effect of nonlinear clustering or Rees-Sciama effect on CMB anisotropiest which might make a significant secondary contribution and complicate the simple picture given by the linear theory. I find that for a wide class of CDM models the effect is of order Delta T/T ~ 10^{-7} - 10^ {-6} and is at least an order of magnitude below the contribution from the primary anisotropies. In the second part of the thesis I investigate how the spatial distribution of light is affected by the matter distribution in the universe through the gravitational lensing effect. I investigate the weak lensing effect on the positions and time delays between multiple images of strong gravitational lenses. I show that although the absolute deviation of an image position relative to its unperturbed position can be of the order of arcminutes, relative positions and time delays are only weakly perturbed, of the order of a few percent. Finally I investigate the weak lensing effect on the correlations in the CMB anisotropies. The effect is most likely negligible on degree angular scales, but becomes more important on arcminute scales and leads to the smoothing of sharp features in the CMB angular power spectrum. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.).
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