Speaker
Description
The fundamental nature of dark matter so far eludes direct detection experiments, but it has left its imprint in the large-scale structure (LSS) of the Universe. Extracting this information requires accurate modelling of structure formation and careful handling of astrophysical uncertainties. I will present new bounds using the LSS on two compelling dark matter scenarios that are otherwise beyond the reach of direct detection today. I will set the strongest limits to-date on the dark matter — proton cross section for dark matter particles lighter than a proton (mass < GeV) [1]. Ultra-light axion dark matter, particles with very low mass (< 10^-19 eV) and astrophysically-sized wavelengths (> kpc), is produced in high-energy models like string theory (“axiverse”). I will rule out axions that are proposed to resolve the so-called cold dark matter “small-scale crisis” (mass ~ 10^-22 eV) using the Lyman-alpha forest (a spectroscopic probe of the intergalactic medium) [2]. Further, I will demonstrate how a mixed axion dark matter model (as produced in the string axiverse) could resolve the S_8 cosmological parameter tension (mass ~ 10^-26 eV) using Planck, ACT and SPT cosmic microwave background and BOSS galaxy survey data [3,4]. The LSS model involves cosmic perturbation theory [3,4], a non-cold dark matter halo model [5] and, to capture the smallest scales, a machine learning model called an “emulator”, trained using hydrodynamical simulations and an active learning technique called Bayesian optimisation [6,7].
