The Hubble Hunter's Guide
By Lloyd Knox, M. Millea. 2019
143 citations recorded by the source corpus.
Measurements of the Hubble constant, and more generally measurements of the expansion rate and distances over the interval 0 < z < 1, appear to be inconsistent with the predictions of the standard cosmological model (ΛCDM) given observations of cosmic microwave background temperature and polarization anisotropies. Here we consider a variety of types of departures from ΛCDM that could, in principle, restore concordance among these datasets, and we explain why we find almost all of them unlikely to be successful. We single out the set of solutions that increase the expansion rate in the decade of scale factor expansion just prior to recombination as the least unlikely. These solutions are themselves tightly constrained by their impact on photon diffusion and on the gravitational driving of acoustic oscillations of the modes that begin oscillating during this epoch – modes that project on to angular scales that are very well measured. We point out that a general feature of such solutions is a residual to fits to ΛCDM, like the one observed in Planck power spectra. This residual drives the modestly significant inferences of angular-scale dependence to the matter density and anomalously high lensing power, puzzling aspects of a data set that is otherwise extremely well fit by ΛCDM.
Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics
View Paper: https://www.semanticscholar.org/paper/342b38d1eb38097029219e68d11569bdbf311cdf
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Citations in the corpus
- Rock ‘n’ roll solutions to the Hubble tension (2019, methodology): “This implies that in order to accommodate a value of H 0 that is compatible with the local measurements (and larger than the Planck ΛCDM best fit [25]), r s has to be modified [40–42].”
- Hubble Tension: The Evidence of New Physics (2023, methodology): “The estimation of H0 from the CMB data proceeds in three steps [100,101]: (1) determine the baryon density and matter density to allow for the calculation of the sound horizon size (rs); (2) infer θs from the spacing between the acoustic peaks to determine the comoving angular diameter distance to l”
- The expansion of the Universe is faster than expected (2020, methodology): “Miras are variable, red giant stars recently pressed into service to measure H0 as a check on both Cepheids and TRGB and yield H0=73.3±3.9 km s-1 Mpc-1 using new HST observations and the previously discussed geometric distances [8].”