Beyond ΛCDM
: current and future constraints on alternative cosmological models

Student thesis: Doctoral Thesis

Abstract

The widely accepted standard model of cosmology consisting of a cosmological constant, Λ, and cold dark matter, or ΛCDM, suffers from many well-known problems which motivate the study of alternative models. This thesis is an exploration of some of these alternatives, focusing in particular on the interacting vacuum scenario. In this scenario, vacuum energy and cold dark matter are allowed to exchange energy.
We perform a detailed study of models within the interacting vacuum scenario, using Markov chain Monte Carlo methods to constrain the parameter space using the latest observational data. When comparing the alternative models to ΛCDM, we find some cases which are weakly favoured over the standard cosmological model, although the tensions present within ΛCDM remain mostly unresolved.
We then move to forecasting future constraints on another fundamental aspect of cosmology: the distance duality relation. We create and use mock datasets of standard sirens, baryon acoustic oscillations and Type Ia supernovæ to forecast constraints on a violation of the distance duality relation due to photon–axion mixing, uncovering a potential smoking gun for modified gravity models with a particular screening phenomenology.
Date of AwardJan 2021
Original languageEnglish
SupervisorDavid Wands (Supervisor), Marco Bruni (Supervisor) & Robert Crittenden (Supervisor)

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