Investigating the Hubble Tension with an Axion-Photon Coupling
Gonzalez, Mark C.
2020
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Hubble's Law and the corresponding Hubble Parameter H are of fundamental importance to our understanding of cosmology. H_0, the value of H today, can be determined through two independent methods, one which uses late-time, model independent data and another which utilizes early universe, model-dependent measurements. However, there is a serious discrepancy in the values measured through these two ... read moremethods and this discrepancy has only grown in recent years. If one assumes that this discrepancy, known as the "Hubble Tension", is not due to unknown systematic errors in the measurements, then one can begin to consider modifications to the standard Lambda-CDM cosmology that are aimed at alleviating this tension. This work considers a modification to Lambda-CDM through the introduction of a very light axion field. Due to Hubble friction, this term acts as vacuum energy in the early universe and leads to an increase in H_0. This new component must dilute quickly prior to recombination, which is achieved by coupling the axion to electromagnetism (or hidden sector photons). This coupling leads to parametric resonance of photons after the axion becomes dynamical. This model is motivated by similar scalar field, axion-based solutions to the Hubble Tension, however this model represents a mechanism that is better motivated from a microscopic physics perspective. The cosmological predictions of this model are investigated through an effective parametrization of the equation of state. Using a Markov Chain Monte Carlo analysis, it is shown that this parametrization shows a mild improvement compared to Lambda-CDM, however further investigation is necessary to determine the efficacy of this model.
Advisor: Professor Mark Hertzbergread less - ID:
- 37720s93b
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