Another Observational Tension With The ΛCDM Model (And Recap Of CDM Fails)

I didn't recognize the implications of this paper for the ΛCDM Model when I saw the abstract in passing when the preprint was released a couple of months ago. Hat tip to Madeleine Birchfield for flagging it. 

The paper argues that the predicted value of the growth index in the ΛCDM Model, that measures the growth of large scale structure, is in strong (4.2 sigma) tension with observations, given the model's measured parameters.

This adds one more observational challenge to the roughly 33 other independent observational challenges to the ΛCDM Model which are already known detailed in previous posts at this blog:

* January 25, 2021 (summarizing the main known observational challenges know to me on that date including compact gravitational lensing in clusters, KIDS evidence of less clumpy structure than predicted, Hubble tension, the wrong DM halo shapes, excessively tight DM-ordinary matter correlations, the unexpected relationship between DM proportion and galaxy shape, satellite galaxies in the galactic plane, too few satellite galaxies, unexpected relationship between bulge mass and number of satellite galaxies, the halo mass function, impossible early galaxies, the EDGES 21 cm result, evidence for an external field effect, the universe is not homogeneous and isotropic, no dark matter galaxies, lack of X-ray emissions in low surface brightness galaxies, there are too few galaxy clusters, it gets globular cluster formation wrong, doesn't explain apparent wide binary star discrepancies, colliding clusters are too common and too fast, the cosmic coincidence problem, dark energy measurement issues, non-detection of DM particles by myriad means shrinking their possible parameter space, few ex ante predictions, gravitational alternatives to DM have made ex ante predictions and solve some of the other problems), 

* February 23, 2021 (missing satellites), 

* March 17, 2021 (the EDGES 21 cm result), 

*August 23, 2021 (DM scaling exponent in clusters), 

* September 23, 2021 (mean separation of void galaxies), 

* December 21, 2021 (Hubble tension), 

* March 11, 2022 (questioning one possible observational conflict from the EDGES 21 cm result), 

* March 14, 2022 (Hubble, structure growth and other cosmological parameter tensions), 

* July 15, 2022 (Chandrasekhar dynamical friction, satellite galaxies plane, cluster collisions, Hubble tension/KBC void, spiral galaxy thickness, impossible early galaxies), 

* July 26, 2022 (impossible early galaxies),

* January 3, 2023 (early star formation efficiency), 

* February 2, 2023 (impossible early galaxies),

* March 2, 2023 (impossible early galaxies),

* March 7, 2023 (satellites of satellites and weak feedback effects), and

* March 17, 2023 (ruling out predicted NFW spike at center of Milky Way).

We present evidence for a suppressed growth rate of large-scale structure during the dark-energy dominated era.

Modeling the growth rate of perturbations with the ``growth index'' γ, we find that current cosmological data strongly prefer a higher growth index than the value γ=0.55 predicted by general relativity in a flat ΛCDM cosmology.

Both the cosmic microwave background data from Planck and the large-scale structure data from weak lensing, galaxy clustering, and cosmic velocities separately favor growth suppression. When combined, they yield γ=0.633+0.025−0.024, excluding γ=0.55 at a statistical significance of 3.7σ. The combination of f σ(8) and Planck measurements prefers an even higher growth index of γ=0.639+0.024−0.025, corresponding to a 4.2σ-tension with the concordance model.

In Planck data, the suppressed growth rate offsets the preference for nonzero curvature and fits the data equally well as the latter model. A higher γ leads to a higher matter fluctuation amplitude S(8) inferred from galaxy clustering and weak lensing measurements, and a lower S(8) from Planck data, effectively resolving the S(8) tension.

Nhat-Minh Nguyen, Dragan Huterer, Yuewei Wen, "Evidence for suppression of structure growth in the concordance cosmological model" arXiv:2302.01331 (February 2, 2023).