Misc,
Consistency of the local Hubble constant with the cosmic microwave background
(2019)cite arxiv:1906.12347Comment: 4 pages, 1 figure; comments welcome.
Abstract
A significant tension has become manifest between the current expansion rate
of our Universe measured from the cosmic microwave background by the Planck
satellite and from local distance probes, which has prompted for
interpretations of that as evidence of new physics. Within conventional
cosmology a likely source of this discrepancy is identified here as a matter
density fluctuation around the cosmic average of the 40 Mpc environment in
which the calibration of Supernovae Type Ia separations with Cepheids and
nearby absolute distance anchors is performed. Inhomogeneities on this scale
easily reach 40% and more. In that context, the discrepant expansion rates
serve as evidence of residing in an underdense region of $\delta_\rm
env\approx-0.5\pm0.1$. The probability for finding this local expansion rate
given the Planck data lies at the 95% confidence level. Likewise, a
hypothetical equivalent local data set with mean expansion rate equal to that
of Planck would not gain strong preference over the actual data in the
respective Bayes factor. These results therefore suggest consistency between
the local and Planck measurements of the Hubble constant. Generally accounting
for the environmental uncertainty, the local measurement may be reinterpreted
as a constraint on the cosmological Hubble constant of $H_0=(76.5\pm5.5)$
km/s/Mpc for the mean and standard deviation or $H_0=74.7^+5.8_-4.2$
km/s/Mpc in terms of median and 68% confidence bounds. The current simplified
analysis may be augmented with the employment of the full available data sets,
an impact study for the immediate $łesssim10$ Mpc environment of the distance
anchors, more prone to inhomogeneities, as well as expansion rates measured by
gravitational waves, currently limited to the same 40 Mpc region, and local
galaxy motions.
