Seminarium "Teoria cząstek elementarnych i kosmologia"

Gravitational lensing time delays were used in recent analyses to infer the cosmological Hubble parameter H0, finding results that exacerbate the tension between late- and early-type determinations of H0. We show that an approximate local version of the lensing mass sheet degeneracy could bias these measurements. In particular, a core component in the lens galaxy density profile would bias H0 in the right direction to resolve the lensing H0 tension. As one possible physical mechanism to generate such cores, we consider ultralight dark matter, for which galactic cores are understood to arise by dynamical relaxation. Cores of roughly the required properties would naturally arise if an ultralight axion, produced via simple vacuum misalignment, makes up a fraction of order ten percent of dark matter.
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