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  • 2016wangphd

    Final published version, 7.87 MB, PDF document

    Available under license: CC BY-ND: Creative Commons Attribution-NoDerivatives 4.0 International License

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Spectator fields and their imprints on the Cosmic Microwave Background

Research output: ThesisDoctoral Thesis

Publication date2016
Number of pages182
Awarding Institution
  • Lancaster University
<mark>Original language</mark>English


When a subdominant light scalar field ends slow roll during inflation, but well after the Hubble exit of the pivot scales, it may determine the cosmological perturbations. This thesis investigates how such a scalar field, the spectator, may leave its impact on the Cosmic Microwave Background (CMB) radiation and be consequently constrained. We first introduce the observables of the CMB, namely the power spectrum Pζ , spectral index ns and its running dns/d ln k, the non-Gaussianities fNL, gNL and τNL, and the lack of isocurvature and polarization modes. Based on these studies, we derive the cosmological predictions for the spectator scenario, revealing its consistency with the CMB for inflection point potentials, hyperbolic tangent potentials, and those with a sudden phase transition. In the end, we utilize the spectator scenario to explain the CMB power asymmetry, with a brief tachyonic fast-roll phase.