The search for dark matter offers the possibility for rich new physics that deepens our understanding of the Universe. The ultra-light axion is a compelling candidate that is motivated, e.g., by the string theory "axiverse" and as a possible solution to the so-called "small-scale crisis" of the cold dark matter model. I will present new, robust bounds on the axion mass that improve by an order of magnitude over previous studies and significantly exclude the canonical mass scale of 10^-22 eV. The bounds exploit new spectroscopic observations of high-redshift (z > 5) quasars and absorption features formed in the intergalactic medium (IGM) -- called the "Lyman-alpha forest".
In order to address the challenge of robustly marginalising the uncertain astrophysics of the IGM, I will present a new framework for dark matter bounds using cosmological data. This utilises a novel "emulator" for the effect of dark matter models on the power spectrum. I will discuss how the application of active learning (Bayesian emulator optimisation) can ensure robust, converged parameter inference from a limited number of expensive simulations.
Join Zoom Meeting https://carnegiescience.zoom.us/j/97435869710