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Gravitational lensing time delays offer an avenue to measure the Hubble parameter $H_0$, with some analyses suggesting a tension with early-type probes of $H_0$. The lensing measurements must mitigate systematic uncertainties due to the mass modelling of lens galaxies. In particular, a core component in the lens density profile would form an approximate local mass sheet degeneracy and could bias $H_0$ in the right direction to solve the lensing tension. We consider ultralight dark matter as a possible mechanism to generate such galactic cores. We show that cores of roughly the required properties could arise naturally if an ultralight axion of mass $msim10^{-25}$ eV makes up a fraction of order ten percent of the total cosmological dark matter density. A relic abundance of this order of magnitude could come from vacuum misalignment. Stellar kinematics measurements of well-resolved massive galaxies (including the Milky Way) may offer a way to test the scenario. Kinematics analyses aiming to test the core hypothesis in massive elliptical lens galaxies should not, in general, adopt the perfect mass sheet limit, as ignoring the finite extent of an actual physical core could lead to significant systematic errors.
It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with $m_asim 10^{-22}text{eV}$ are a preferred dark matter candidate. However, comparisons to theoretical predi
A number of proposed and ongoing experiments search for axion dark matter with a mass nearing the limit set by small scale structure (${cal O} ( 10 ^{ - 21 } {rm eV} ) $). We consider the late universe cosmology of these models, showing that requirin
Riess et al (2018c) have claimed there exist seven problems in the analyses presented by Shanks et al (2018) where we argue that there is enough uncertainty in Cepheid distances and local peculiar velocity fields to explain the current tension in $H_
There is an $approx9pm2.5$% tension between the value of Hubbles Constant, $H_0=67.4pm0.5$km,s$^{-1}$Mpc$^{-1}$, implied by the {it Planck} microwave background power spectrum and that given by the distance scale of $H_0=73.4pm1.7$km,s$^{-1}$Mpc$^{-1
It is currently thought that the early dark energy (EDE) resolution of the Hubble tension will inevitably suffer inconsistency with the large scale structure data (quantified as $S_8$). However, if this so-called $S_8$ tension is physical, it might b