  One of the major objectives of this dissertation has been the seek for
inflationary models, coming from supersymmetric theories, which are compatible
with recent cosmological data and, more specifically, with measurements of the
spectral index from the WMAP3 data. A particular particle physics model, the
extended SUSY Pati-Salam model with Yukawa quasi-unification, was examined
thoroughly with respect to its cosmology and it was found that it incorporates
a number of inflationary scenarios which can become compatible with recent
data. The study of these scenarios brought out variations of cosmological
models which might be important in cosmological research.
