Date of Award
Doctor of Philosophy (PhD)
Physics & Astronomy
In this dissertation, we introduce and investigate a general framework to describe the dynamics of the early universe. This mechanism is based on spontaneously broken conformal symmetry; we find that spectator fields in the theory can acquire a scale invariant spectrum of perturbations under generic conditions. Before introducing the conformal mechanism, we first consider the landscape of cosmologies involving a single scalar field which can address the canonical early universe puzzles. We find that, generically, single field non-inflationary solutions become strongly-coupled. We are therefore led to consider theories with multiple fields. We introduce the conformal mechanism via specific examples before constructing the most general effective theory for the conformal mechanism by utilizing the coset construction familiar from particle physics to construct the lagrangian for the Goldstone field of the broken conformal symmetry. This theory may be observationally distinguished from inflation by considering the non-linearly realized conformal symmetries. We systematically derive the Ward identities associated to the non-linearly realized symmetries, which relate (N+1)-point correlation functions with a soft external Goldstone to N-point functions, and discuss observational implications, which cannot be mimicked by inflation. Finally, we consider violating the null energy condition (NEC) within the general framework considered. We show that the DBI conformal galileons, derived from the world-volume theory of a 3-brane moving in an Anti-de Sitter bulk, admit a background which violates the NEC. Unlike other known examples of NEC violation, such as ghost condensation and conformal galileons, this theory also admits a stable, Poincaré-invariant vacuum. However, perturbations around deformations of this solution propagate superluminally.
Joyce, Austin, "Conformality Lost: Broken Symmetries in the Early Universe" (2013). Publicly Accessible Penn Dissertations. 767.