Thesis (Ph.D.) - Cairo University - Faculty of Science - Department of Astronomy and Meteorology

It is known that standard cosmology su{uFB00}ers from some problems. Among suggested solutions are f(R) and f(T) theories in which energy-momentum distri- bution is described by a phenomenological second order tensor. In a version of absolute parallelism (AP-) geometry, a pure geometric {uFB01}eld theory is constructed in the context of the Uni{uFB01}cation Principle. This principle guarantees writing every quantity in the theory using the building blocks (BB) of the AP-geometry only. Physical analysis of the theory shows that the theory represents a uni{uFB01}ed gravity and electromagnetic {uFB01}eld. Geometric expressions for Poisson equation for gravity and electromagnetic {uFB01}elds are obtained. Also, we show that the suggested theory has a successful GR-limit. A general di{uFB00}erential identity is derived in a modi{uFB01}ed version of AP-geometry. The importance of this di{uFB00}erential identity is its relation to conservation in the context of geometrization philosophy. Applications of the suggested theory in the domain of cosmology, satisfying the cosmological principle, solve {uFB02}atness and particle horizons problems

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