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SUMMARY:Gravitational lensing H0 tension from ultralight axion galactic co
 res - Kfir Blum (Weizmann Institute of Science)
DTSTART:20210524T120000Z
DTEND:20210524T130000Z
UID:TALK158920@talks.cam.ac.uk
CONTACT:James Bonifacio
DESCRIPTION:Gravitational lensing time delays offer an avenue to measure t
 he Hubble parameter H0\, with some analyses suggesting a tension with earl
 y-type probes of H0. The lensing measurements must mitigate systematic unc
 ertainties due to the mass modelling of lens galaxies. In particular\, a c
 ore component in the lens density profile would form an approximate local 
 mass sheet degeneracy (MSD) and could bias H0 in the right direction to so
 lve the lensing tension. We consider ultralight dark matter (ULDM) as a po
 ssible mechanism to generate such galactic cores. We show that cores of ro
 ughly the required properties could arise naturally if an ultralight axion
  of mass m~10^-25 eV makes up a fraction of order ten percent of the total
  cosmological dark matter density. A relic abundance of this order of magn
 itude could come from vacuum misalignment. Stellar kinematics measurements
  of well-resolved massive galaxies (including the Milky Way) may offer a w
 ay to test the scenario. Kinematics analyses aiming to test the core hypot
 hesis in massive elliptical galaxies should not\, in general\, adopt the p
 erfect MSD limit\, as ignoring the finite extent of an actual physical cor
 e could lead to significant systematic errors.
LOCATION:CMS\, Pav. B\, CTC Common Room (B1.19) [Potter Room]
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