Aspects of grand unified and string phenomenology

Explored in this report is the essential interconnectedness of Grand Unified and String Theoretic Phenomenology. In order to extract a modeled connection to low-energy physics from the context of superstring theory, it is presently necessary to input some preferred region of parameter space in which to search. This need may be well filled by a parallel study of Grand Unification, which is by contrast in immediate proximity to a wealth of experimental data. The favored GUT so isolated may then reasonably transfer this phenomenological correlation to a string embedding, receiving back by way of trade a greater sense of primary motivation, and potentially enhanced predictability for parameters taken as input in a particle physics context. The Flipped SU(5) GUT will be our preferred framework in which to operate and first receives an extended study in a non-string derived setting. Of particularly timely interest are predictions for super-particle mass ranges and the interrelated question of proton decay lifetime. Corrections to such a picture under the lift to a string embedding are also considered. Two principal approaches to string model building are next treated in turn: the Heterotic Free Fermionic construction and Intersecting D-branes in Orientifold compactifications. In both contexts, a summary of existing constructions, extensions to known procedures, and original phenomenological contributions are described.