Browsing by Subject "Axion"

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    Gauge Field Amplification during Axion Inflation
    (2018-08) UNAL, CANER
    This thesis studies the interaction of different fields during inflation and resultant phenomenology at different scales. It particularly focuses on one of the most well motivated inflationary models, called Axion inflation. Axions are pseudo-scalars that possess the shift symmetry at least at the approximate level, which protects their potential from quantum corrections and elevates them as a strong inflaton candidate. However, in the particle inventory of UV complete theories, axion particles are abundant, which motivates studying axions as inflaton or spectator field during inflation. In this work, we study a chiral shift symmetric dimension-five operator arising naturally in any axion theory. Due to this coupling, the gauge field'Äôs dispersion relation is modified and one helicity of the gauge field is produced abundantly as a function of a dimensionless parameter proportional to speed of the axion. This breaks the parity conservation. Furthermore, this amplified gauge quanta inversely decays (ie. sources back) to scalar and tensor degrees of freedom via two-to-one way; hence, the sourced perturbations obey non-Gaussian statistics. These sourced modes leave unique imprints on cosmological observables such as : Chiral gravitational wave (GW) background, large tensor non-Gaussianity, non-zero TB and EB correlators, detectable GW background at interferometer scales and the production of primordial black holes.
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    Holographic and Composite Models of the Axion
    (2021-07) Nguyen, Minh
    The axion, first proposed to solve the absence of a neutron electric dipole moment, is also an excellent dark matter candidate. If the axion is composite, it must be bound by a novel strong interaction. Some strongly-coupled models, mathematically intractable until now, are recently discovered to be calculable through a mapping onto 5-dimensional gravity. We propose a series of composite and extra dimensional axion models. A basic 5-dimensional model first incorporates the known forces while keeping the axion consistent with gravitational corrections. More sophisticated extensions address other problems in particle physics unrelated to the axion, providing nontrivial predictions that can be tested experimentally. We further propose a composite model that incorporates both the Higgs boson and the axion. By enlarging the color gauge group, we provide a consistent procedure to raise the axion masses as high as TeV collider energy scales, further motivating experimental searches for axion-like particles.