Phenomenology of axion inflation with non-Abelian gauge fields
It is believed that our Universe experienced a very early period of accelerated expansion, known as cosmic inflation, needed to reconcile the latest observations with our current physical understanding. Even though the exact mechanism responsible for such a phenomenon still eludes us, we know it can be realized within a quantum field theory framework. The simplest realization is then provided by a single scalar field displaced from the minimum of its potential and slowly moving towards it.
A theoretically well-motivated inflationary candidate is given by natural inflation, a model with a single pseudoscalar field where the potential takes a characteristic sinusoidal shape. Although with a strong theoretical foundation, this setup is in contrast with the latest experimental bounds and needs to be extended accordingly in order to constitute a potentially viable inflationary model.
Martino Michelotti addresses this by considering a multi-field extension of natural inflation, where the axion is coupled with gauge fields. A main focus is the study of additional sources of friction slowing down the axion field dynamics, necessary in order to sustain a long enough period of inflation along with predictions in agreement with observations. Another point of interest is the investigation of the behaviour of these models in the presence of non-linearities, in the case primordial quantum fluctuations originating during inflation become very large.
The work reported in this thesis, combined with future observations, will contribute towards a better understanding of the physics of the early Universe.