Speaker
Description
The fundamental nature of dark matter so far eludes direct detection experiments, but it has left its imprint in the cosmic large-scale structure. Ultra-light axions (ULAs; masses m < 10^-18 eV) are motivated by axiverse considerations. Searching for ULAs requires accurate modelling of axion structure formation including wave effects, careful handling of astrophysical uncertainties and consistent observations in independent cosmological probes. I will review a multi-scale, multi-epoch test of ULAs combining observations of the cosmic microwave background, galaxy clustering (redshift z < 2), the Lyman-alpha forest (2 < z < 5) and the high-redshift (z > 5) galaxy UV luminosity function from the Hubble and Webb Space Telescopes. I will show that both the S_8 cosmological parameter discrepancy and a new five-sigma tension in inference of the small-scale matter power spectrum can be resolved by a contribution of ULAs with m ~ 10^-25 eV. I will discuss prospects for adjudicating the viability of axion solutions in observations of the galaxy and Milky Way sub-structure distributions in the transformative Vera Rubin Observatory.
