This online-only conference featured 5 days of talks by cosmologists from 22-Jun-2020 to 26-Jun-2020. For anyone interested in the H0 tension problem, this is an excellent and highly recommended resource. Here are links to key resource information covering the conference.
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A KITP-UCSB program running from Jan 6 to Mar 13, 2020 is an excellent resource for topics related to primordial universe cosmology (e.g., inflation, reheating (aka the Hot Big Bang), baryogenesis, non-gaussianity, dark sectors, cosmological sources of gravitational waves, Hubble tension, etc). The program agenda with links to videos and slides is here.
I'd like to point out an excellent overview talk from this program by Raphael Flauger on Feb. 28 that reviews Hubble measurement physics and results from each of the major determination methods and discusses current status on Hubble tension. The video for Flauger's talk is here. That page does not have the talk slides (at least not yet anyway) but the slides are available in PDF format here. Update: the slides are also now available on the KITP video page. Here is a PDF of the slides.
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Link to paper: [2003.07355] Early Dark Energy Does Not Restore Cosmological Concordance, by J. Colin Hill, Evan McDonough, Michael W. Toomey, Stephon Alexander
Updates since this was originally posted:
Background
Going back at least several years [1], but increasingly since late-2018 [2-7], there has been growing theoretical interest for the Hubble tension issue that suggests new physics models may be needed for the early universe prior to recombination that do not cause changes to late time cosmology, since that is tightly-constrained [4, 8].
For example, papers [2, 5] propose models for a new form of early dark energy (EDE) present at z ≳ 3000 that then dilutes away, resulting in a reduced sound horizon at decoupling. This results in a larger inferred $H_0$ value from CMB data versus Planck results, thus reducing the disparity between early and late time $H_0$ results.
These EDE proposals for resolving $H_0$ tension were characterized as being somewhere on the spectrum between “most plausible” [3] to “least unlikely” [4].
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I had in mind to create a list of recent papers I found of interest that also had an author's talk available and in some cases a review. But after starting this post, I realized it's really so much better to have this data input into the recently initiated and excellent ResearchSeminars.org site, which has great listing and filtering capabilities and is becoming widely used. So I volunteered to the organizers of two cosmology talk series to input their data: Cosmology Talks on youtube hosted by Shaun Hotchkiss and CosmoConβ on youtube, aka Cosmology from Home. The target audience for these are researchers in the field. Now at the Research Seminars site, both Cosmology Talks and CosmoConβ are listed with all their current talks. Also, the Cosmology Talks series includes indexed links to the times of major sections of each talk as a convenience and helpful reference feature.
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New developments since this post was originally created:
This is about two recent papers with the premise that H0 tension resolution could come from new physics at early times before recombination.
The first paper, Sounds Discordant: Classical Distance Ladder & ΛCDM-based Determinations of the Cosmological Sound Horizon [arxiv:1811.00537] is based on looking at the tension in terms of the sound horizon rs. They cite several advantages of doing so: (1) “added insensitivity to extreme changes in the cosmology at z < 0.1, since one does not need to extrapolate to z = 0”, (2) “the ΛCDM predictions for the sound horizon are more robust than those for H0”, (3) “as with the inverse distance ladder, this approach clarifies that reconciliation can not be delivered by altering cosmology at z < 1”, (4) “it serves to clarify that the reconciliation of distance ladder, BAO, and CMB observations via a cosmological solution is likely to include a change to the cosmological model in the two decades of scale factor evolution prior to recombination”, and (5) “σ(rs)/rs from CMB data, assuming ΛCDM, is four times smaller than the σ(H0)/H0 from the same data and assumed model.”
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