Relic Density of Axion Dark Matter in Standard and Non-Standard Cosmological Scenarios

TL;DR

This thesis investigates how non-standard cosmological scenarios influence the production and relic density of axion dark matter, revealing significant effects on oscillation temperature, density dilution, and axion-photon coupling.

Contribution

It provides a detailed analytical and numerical analysis of axion relic density considering non-standard cosmologies, expanding understanding of axion parameter space.

Findings

Oscillation temperature is strongly affected by non-standard cosmology.

Relic density of axions is diluted due to entropy injection from decay of the new fluid.

The parameter space for axion dark matter is modified in non-standard cosmological models.

Abstract

In this master's thesis we study the production of axion dark matter through the so-called misalignment mechanism by considering that during that time, the universe was dominated by a new kind of fluid, different than radiation. We perform a very detailed analysis of the oscillation temperature and the relic density today, both analytically and numerically. Our findings show that on the one hand, the oscillation temperature is strongly influenced by the non-standard cosmology, affecting the relic density, and on the other hand, the energy density of the axion gets diluted, because the new fluid eventually decays, injecting entropy into the thermal bath. We find the predicted parameter space of axion dark matter for different non-standard cosmologies and we show its impact on the coupling of axions to two photons.