Hunting for ultralight dark matter with cosmographic H0 signal

If ultralight boson fields exist, then vacuum misalignment populates them with nonzero relic abundance. For a broad range of particle mass m the field condenses into fuzzy cores in massive galaxies. We use numerical simulations to test this idea, extending previous work [Blum and Teodori, Phys. Rev. D 104, 123011 (2021)PRVDAQ2470-001010.1103/PhysRevD.104.123011] and focusing on ultralight dark matter (ULDM) that makes up a subdominant fraction of the total dark matter density, consistent with observational constraints. Our simulations mimic galactic halos and explore different initial conditions and levels of sophistication in the modeling of the halo potential. For m∼10-25 eV ULDM cores act as approximate internal mass sheets in strong gravitational lensing, and could first be detected using time delays in cosmography, when an H0 prior is assumed: a scenario we dub AxionH0graphy. The mass sheet degeneracy is broken by finite core radius and by the dynamical displacement of cores from the halo center of mass, which introduce imaging distortions and restrict the H0 signal limit of AxionH0graphy to m≲5×10-25 eV. Cosmological simulations are called for to sharpen the predicted connection between the amplitude of ULDM galactic cores and the ULDM cosmological fraction.