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Probing Axion Inflation Coupled to U(1) Gauge Fields

Morbelli, Gianmarco (2023) Probing Axion Inflation Coupled to U(1) Gauge Fields. Bachelor's Thesis, Physics.


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This bachelor thesis investigates axion-driven inflation coupled to a generic U(1) gauge field. The intrinsic shift symmetry inherent to axions forbids or highly suppresses possible UV corrections, ensuring a substantial degree of flatness in the inflationary potential over an extended duration. The interplay between the axion and the gauge field significantly affects the dynamics of the axion field, deviating from a homogeneous behavior. Backreaction effects, such as the sourcing of inflaton perturbations through the inverse decay of gauge field fluctuations and contributions to the universe energy density, are analyzed. Curvature perturbations arising from the coupling and their impact on the power spectrum at the superhorizon limit are derived and discussed. The resulting power spectrum is found to exhibit the expected mild scale dependence characteristic of slow-roll inflation. By imposing COBE normalization to the power spectrum, the mutual interaction between the axion and gauge field is highlighted. Specifically, it is found how for ξ ≫ 4, where the parameter ξ is linked to the coupling and growth of gauge field fluctuations, the gauge field contribution to the spectrum becomes dominant and completely surpasses the vacuum fluctuations. Further research directions are proposed: the replication of results can involve considering full scalar and metric perturbations. Additionally, investigating tensor perturbations may provide insights into plausible GW production.

Item Type: Thesis (Bachelor's Thesis)
Supervisor name: Dimastrogiovanni, E. and Roest, D.
Degree programme: Physics
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 17 Jul 2023 11:50
Last Modified: 17 Jul 2023 11:50

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