Cosmology driven by physics beyond the standard model

This dissertation investigates several problems inspired by the interplay of cosmology and theories beyond the Standard Model of particle physics. The first part of this work is a study of time evolution of unstable dS[subscript p] x S[superscript q] configurations with flux in theories of gravity with a cosmological constant. We find that, depending on the flux, these configurations either evolve towards newly identified stable solutions with a smaller final effective cosmological constant, or tend toward decompactication of the internal sphere. In the second part, we investigate the problem of evolution of vacuum bubbles in inhomogeneous backgrounds. It is expected that the process of inflation will signifcantly smooth out spatial inhomogeneities. However, the initial conditions for inflation are often taken in the already homogeneous and isotropic FRW form, even though it is assumed that initial homogeneity is not necessary for the onset of inflation. We determine the effects of certain inhomogeneities, introduced in the curvature of the outside spacetime, on the propagation of bubbles, and how these effects differ depending on whether the perspective taken is that of the outside observer or an observer on the bubble. The last part of the dissertation presents a model for a novel component of the energy density of the universe. The observational limits on the present energy density allow for a component that redshifts like 1/a² and can contribute significantly to the total. We show that one possible origin for such a contribution is that the universe has a toroidal topology with "wound" scalar fields around its cycles.