Beschreibung
Ultralight axions are a well-motivated dark matter candidate whose large de Broglie wavelength suppresses the growth of structure on small scales, making cosmological observations a powerful probe of their existence. Realizing the full constraining power of current and upcoming surveys, however, requires accurate predictions of nonlinear structure formation in mixed cold dark matter–ultralight axion cosmologies. I will present recent advances in modelling the nonlinear matter distribution using a simulation-calibrated halo model and discuss how these developments enable precision tests of ultralight axion dark matter across multiple cosmological observables. I will highlight applications to weak gravitational lensing and cosmic voids, demonstrating how complementary probes improve sensitivity to the axion mass and abundance while providing robust forecasts for next-generation surveys. Finally, I will share new constraints from gravitational lensing measurements by Planck, the Atacama Cosmology Telescope, and SPT-3G, which provide the strongest limits to date on ultralight axions in the mass range (10^{-26})–(10^{-24.5},\mathrm{eV}). These results significantly narrow the viable parameter space for ultralight axion dark matter and illustrate the growing power of nonlinear cosmological probes to test fundamental physics beyond LambdaCDM.