%0 Generic %1 vagnozzi2023seven %A Vagnozzi, Sunny %D 2023 %K astronomy cosmology hubble_constant hubble_tension %R 10.3390/universe9090393 %T Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension %U http://arxiv.org/abs/2308.16628 %X The Hubble tension has now grown to a level of significance which can no longer be ignored and calls for a solution which, despite a huge number of attempts, has so far eluded us. Significant efforts in the literature have focused on early-time modifications of $Łambda$CDM, introducing new physics operating prior to recombination and reducing the sound horizon. In this opinion paper I argue that early-time new physics alone will always fall short of fully solving the Hubble tension. I base my arguments on seven independent hints, related to 1) the ages of the oldest astrophysical objects, 2) considerations on the sound horizon-Hubble constant degeneracy directions in cosmological data, 3) the important role of cosmic chronometers, 4) a number of ``descending trends'' observed in a wide variety of low-redshift datasets, 5) the early integrated Sachs-Wolfe effect as an early-time consistency test of $Łambda$CDM, 6) early-Universe physics insensitive and uncalibrated cosmic standard constraints on the matter density, and finally 7) equality wavenumber-based constraints on the Hubble constant from galaxy power spectrum measurements. I argue that a promising way forward should ultimately involve a combination of early- and late-time (but non-local -- in a cosmological sense, i.e. at high redshift) new physics, as well as local (i.e. at $z 0$) new physics, and I conclude by providing reflections with regards to potentially interesting models which may also help with the $S_8$ tension.

@misc{vagnozzi2023seven, abstract = {The Hubble tension has now grown to a level of significance which can no longer be ignored and calls for a solution which, despite a huge number of attempts, has so far eluded us. Significant efforts in the literature have focused on early-time modifications of $\Lambda$CDM, introducing new physics operating prior to recombination and reducing the sound horizon. In this opinion paper I argue that early-time new physics alone will always fall short of fully solving the Hubble tension. I base my arguments on seven independent hints, related to 1) the ages of the oldest astrophysical objects, 2) considerations on the sound horizon-Hubble constant degeneracy directions in cosmological data, 3) the important role of cosmic chronometers, 4) a number of ``descending trends'' observed in a wide variety of low-redshift datasets, 5) the early integrated Sachs-Wolfe effect as an early-time consistency test of $\Lambda$CDM, 6) early-Universe physics insensitive and uncalibrated cosmic standard constraints on the matter density, and finally 7) equality wavenumber-based constraints on the Hubble constant from galaxy power spectrum measurements. I argue that a promising way forward should ultimately involve a combination of early- and late-time (but non-local -- in a cosmological sense, i.e. at high redshift) new physics, as well as local (i.e. at $z \sim 0$) new physics, and I conclude by providing reflections with regards to potentially interesting models which may also help with the $S_8$ tension.}, added-at = {2023-09-02T22:24:34.000+0200}, author = {Vagnozzi, Sunny}, biburl = {https://www.bibsonomy.org/bibtex/2e0300e19c245863b87379c43e6a97ffa/tabularii}, description = {Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension}, doi = {10.3390/universe9090393}, interhash = {5365e14da1c0e1db72f573ded8f41020}, intrahash = {e0300e19c245863b87379c43e6a97ffa}, keywords = {astronomy cosmology hubble_constant hubble_tension}, note = {cite arxiv:2308.16628Comment: 39 pages, 18 sub-figures arranged into 11 figures, most of which reproduced (with permission) from other works, many references, "alone" is the keyword here. A very pictorial summary of the whole paper is in Fig. 11, not made by me. Accepted for publication in Universe as an invited opinion/review paper in the special issue "Modified Gravity Approaches to the Tensions of \Lambda CDM"}, timestamp = {2023-09-02T22:24:34.000+0200}, title = {Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension}, url = {http://arxiv.org/abs/2308.16628}, year = 2023 }