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Register a new user$H_0$ Tension: Response to Riess et al arXiv:1810.03526
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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 $H_0$. Here, we take each of the Riess et al (2018c) points in turn and suggest that either they do not apply or that the necessary caveats are already made by Shanks et al (2018). We conclude that the main point to be inferred from our analyses still stands which is that previous claims by Riess et al (2018b) that Gaia parallaxes confirm their Cepheid scale are, at best, premature in advance of further improvements in the Gaia astrometric solution.
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We offer a brief response to the criticisms put forward by Cusin et al in arXiv:1811.03582 about our work arXiv:1810.13435 and arXiv:1806.01718, emphasising that none of these criticisms are relevant to our main results.
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$^{-1}$. But with a plausible assumption about a {it Gaia} DR2 parallax systematic offset, we find that {it Gaia} parallax distances of Milky Way Cepheid calibrators are $approx12-15$% longer than previously estimated. Similarly, {it Gaia} also implies $approx4.7pm1.7$% longer distances for 46 Cepheids than previous distances on the scale of Riess et al. Then we show that the existence of an $approx150$h$^{-1}$Mpc `Local Hole in the galaxy distribution implies an outflow of $approx500$km,s$^{-1}$. Accounting for this in the recession velocities of SNIa standard candles out to $zapprox0.15$ reduces $H_0$ by a further $approx1.8$%. Combining the above two results would reduce the distance scale $H_0$ estimate by $approx7$% from $H_0approx73.4pm1.7$ to $approx68.9pm1.6$ km,s$^{-1}$Mpc$^{-1}$, in reasonable agreement with the {it Planck} value. We conclude that the discrepancy between distance scale and {it Planck} $H_0$ measurements remains unconfirmed due to uncertainties caused by {it Gaia} systematics and an unexpectedly inhomogeneous local galaxy distribution.
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.
In Jiang et al. (2020), we reported a possible bright flash (hereafter GN-z11-flash) from a galaxy GN-z11 at z ~ 11. Recently, Steinhardt et al. (2021; arXiv:2101.12738) found 27 images with transient signals in Keck MOSFIRE archival data and claimed that GN-z11-flash was more likely from a moving object in our Solar system. We show that the Steinhardt et al.s definition of the chance probability and their methodology of finding GN-z11-flash-like transients are problematic in several aspects. In particular, none of their transients is analogous to GN-z11-flash, and none of them is positionally coincident with a known object in their imaging data. In Jiang et al., we performed a comprehensive analysis of the origin of GN-z11-flash and ruled out, to the best of our knowledge, the possibility of known man-made objects or moving objects in the Solar system, based on all available information and our current understanding of these objects. Steinhardt et al. did not use such information and did not analyse the GN-z11-flash event itself. The majority of their transients are apparently low-Earth orbit satellites or aircrafts. Therefore, their analysis can neither prove nor disprove our results. Finally, we present a method to estimate the chance probability of finding GN-z11-flash-like transients in archival data. Based on this method and the archival data used by Steinhardt et al., we obtain a loose upper limit of the probability that actually support the original results of Jiang et al. (2020).
In a comment on arXiv:1006.5070v1, Drechsler et al. present new band-structure calculations suggesting that the frustrated ferromagnetic spin-1/2 chain LiCuVO4 should be described by a strong rather than weak ferromagnetic nearest-neighbor interaction, in contradiction with their previous calculations. In our reply, we show that their new results are at odds with the observed magnetic structure, that their analysis of the static susceptibility neglects important contributions, and that their criticism of the spin-wave analysis of the bound-state dispersion is unfounded. We further show that their new exact diagonalization results reinforce our conclusion on the existence of a four-spinon continuum in LiCuVO4, see Enderle et al., Phys. Rev. Lett. 104 (2010) 237207.
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