Fundamental Cosmology in the Era of Surveys: A Multi-scale Numerical Campaign

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We are fortunate to live in a particularly exciting time for cosmology. The next decade will herald the onset of several large-scale surveys of galaxies, designed for the ultimate goal of answering some of the most pressing, outstanding problems in cosmology: What is the nature of the dark matter? What is the underlying physics that drives the accelerated expansion of the Universe? Is there evidence for physics beyond the Standard Model? Addressing these fundamental questions requires a census of galaxies -- in other words, a map of the large-scale structure of the Universe -- that exceeds far beyond what we have available to us at the moment, both in its volume and the precision of the data. Fortunately, planned surveys like the Dark Energy Spectroscopic Instrument (DESI), the Legacy Survey of Space and Time (LSST), Euclid and The Nancy Grace Roman Space Telescope are purpose-built for exactly these demands. In order to make any sense of these large -- and expensive -- data sets, it is necessary to consider them in the context of equally sophisticated theoretical models. My programme, which lies at the nexus of cosmology, particle physics and high-performance computing, will address this need, following three broad scientific questions: What are the new frontiers for probing cosmologies beyond the standard theory? In our best models of the Universe, dark matter and dark energy are thought to dominate, yet our understanding of their nature remains woefully incomplete. I will develop new techniques for probing different theories of dark matter and gravity which take advantage of new observational methods that will soon become feasible. One such example is a method known as "intensity mapping", which characterises the distribution of the first galaxies that formed in the cosmos by mapping the primordial radiation emanating from them. Using state-of-the-art radiation hydrodynamics simulations, my research will, for the first time, characterise the statistics of this radiation under different assumptions for the nature of the dark matter particle, offering a potentially very powerful probe for constraining these theories.How might the interplay between dark and baryonic ("ordinary") matter affect what we infer from future galaxy surveys? Many of the phenomena we expect to measure from upcoming surveys map directly to the underlying cosmological model describing our Universe. On the other hand, these inferences may be altered significantly after accounting for 'feedback' from galaxy formation physics on the clustering of matter. Simulations that model dark matter only are, at present, the standard data sets used to compare theory with observation, and are unable to account for these baryonic effects. Understanding the systematic biases imparted by baryonic processes on the inference of cosmological parameters is of paramount importance in the build-up to next generation surveys. The new generation of simulations my research will produce will create a unique framework to test the standard assumptions that have been made until now. What can we learn about the Universe from our own Galactic backyard? The faint galaxies orbiting the Milky Way are amongst the first generations of structures formed in cosmic history; the tidal debris left over by the subset of these galaxies that have been destroyed by the gravity of the Milky Way lay strewn across night sky, and can be used as tracers of the formation history of our Galaxy. Understanding the Milky Way provides us with a unique opportunity to pin down the uncertain physics of early galaxy formation. My research will also focus on modelling the formation of the first galaxies and will develop a novel approach for tracing their subsequent evolution in the gravitational field of the Milky Way.With the UKRI FLF, I will develop a long-term, multi-scale campaign of numerical simulations that will present an unrivalled theoretical framework to compare against future surveys.