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Title: Cosmological implications of primordial vector fields
Author: Wagstaff, Jacques M.
Awarding Body: Lancaster University
Current Institution: Lancaster University
Date of Award: 2012
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A vector curvaton model for a massive Abelian vector field with a Maxwell type kinetic term is presented and analysed. The model does not suffer from instabilities such as ghosts. A scale-invariant spectrum of superhorizon perturbations can be generated if the mass and kinetic function of the vector field are appropriately varying during inflation. If the vector field remains light until the end of inflation it can generate statistical anisotropy in the spectrum and bispectrum of the curvature perturbation. In this case the non-Gaussianity is predominantly anisotropic, which will be directly tested by the imminent results of the Planck satellite. If, on the other hand, the vector field is heavy by the end of inflation then particle production is isotropic and the vector field alone can give rise to the curvature perturbation. It is demonstrated that when the inflaton modulates the mass and kinetic function of the vector field, the dynamic backreaction leads to a new inflationary attractor solution. On this attractor solution the desired variation of the mass and kinetic function of the vector field are obtained. If the field is massless, or if it remains light until the end of inflation, this attractor solution can also render inflation weakly anisotropic. In other words scale-invariant spectra of vector field perturbations and anisotropic inflation are attractor solutions. The above two characteristics of the attractor solution can source (independently or combined together) significant statistical anisotropy in the curvature perturbation. It is shown that, on this new inflationary attractor solution the inflaton's variation suffers additional impedance. As a result, slow-roll inflation can naturally occur along directions of the scalar potential which would be too steep and curved to support it otherwise. This provides a generic solution to the infamous eta-problem of inflation in supergravity. Moreover, it is shown that, in the new inflationary attractor, the spectral index of the generated curvature perturbations is kept mildly red despite eta of order unity. The above findings are applied to a model of hybrid inflation in supergravity with a generic Kaehler potential. The spectral index of the generated curvature perturbations is found to be 0.97 - 0.98, in excellent agreement with observations. The gauge field can play the role of the vector curvaton after inflation but observable statistical anisotropy requires substantial tuning of the gauge coupling.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available