New inflationary cosmology

The spontaneous symmetry breaking phase transitions in the early universe predicted by grand unified models are studied. Some of these models predict that during the phase transition the universe experienced a period where potential energy dominated the total energy density and caused the size of the universe to increase exponentially with time. It is shown that in special models the exponential expansion can continue even after the phase transition is well underway and, in these cases, once the transition is completed and the universe is describable by the standard Friedmann-Robertson-Walker cosmology, the necessary special conditions of the standard hot big bang model have been realized in a natural way and the monopoles are not overabundant. The general mechanism demonstrated looks promising as a solution to the horizon, flatness, and monopole problems, although specific models considered so far are not completely satisfactory. The standard SU(5) grand unified model and a supersymmetric model which employs the ''Written reverse hierarchy mechanism'' to dynamically generate the grand unification scale are studied in detail