COSMOLOGICAL ANOMALIES SHED LIGHT ON THE DARK SECTOR

Little is known about dark energy and dark matter; but their simple descriptions in the ΛCDM model of cosmology fit numerous datasets well. Recently however, tensions have emerged between the results of different datasets, as have certain unex- pected results. These anomalies may indicate new physics beyond ΛCDM; a revision of how we describe the dark sector. My work uses cosmological anomalies to explore the dark sector. My research resolves perhaps the most exciting tension in cosmology, the Hubble tension, with early dark energy (EDE). I developed two physical models for EDE and find that these models not only solve the Hubble tension, but also fit most cosmolog- ical datasets well. No other solution to the Hubble tension proposed thus far can do both - fully solve the tension while still fitting early and late-time measurements of the Universe. The model that succeeds ΛCDM should solve not only the Hubble tension but also other cosmological tensions such as the S8 anomaly. My research investigates a decaying dark matter model to address both tensions simultaneously but finds the constraints from late-universe observations too stringent to permit a full resolution. I am also building a phenomenological tool to model the dark sector in a widely- used cosmological code. This tool, generalised dark matter, is a powerful formalism capable of emulating the effects of a wide variety of dark matter and dark energy models, simplifying placing constraints on different fundamentally-motivated models. The formalism and two immediate applications of it are discussed. My work also shows that a curious cosmic-ray (CR) measurement likely has an astrophysical explanation rather than one motivated by dark matter. More flux in CR positrons is observed at high energies than expected, indicating new sources for high-energy CR positrons. My work demonstrates that nearby pulsars could source these positrons and it develops a new analysis technique to distinguish dark matter and pulsar sources for CR data. The aforementioned anomalies and many others have persisted in cosmology for years. It may be time to look beyond the standard model of cosmology for new physics and new descriptions of the dark sector