A non-linear solution to the $S_8$ tension?

Abstract

Weak galaxy lensing surveys have consistently reported a lower amplitude for the matter fluctuation spectrum, as measured by the S 8 parameter, than expected in the ΛCDM cosmology favoured by Planck. However, the expansion history follows the predictions of the Planck ΛCDM cosmology to high accuracy, as do measurements of lensing of the cosmic microwave background anisotropies. Redshift space distortion measurements also appear to be consistent with Planck ΛCDM. In this paper, we argue that these observations can be reconciled with the Planck ΛCDM cosmology if the matter power spectrum is suppressed more strongly on non-linear scales than assumed in analyses of weak galaxy lensing. We demonstrate this point by fitting a one-parameter model, characterising a suppression of the non-linear power spectrum, to the KiDS-1000 weak lensing measurements. Such a suppression could be attributed to new properties of the dark matter that affect non-linear scales, or to a response of the matter fluctuations to baryonic feedback processes that are stronger than expected from recent cosmological simulations. Our proposed explanation can be tested using measurements of the amplitude of the matter fluctuation spectrum on linear scales, in particular via high precision redshift space distortion measurements from forthcoming galaxy and quasar redshift surveys.

Exploring the effects of primordial non-Gaussianity at galactic scales

“…This feature may be particularly interesting in view of the S 8 tension and the phenomenological parametrization of ref. [56]. In terms of the halo mass function, NG1and NG2+ tend to overproduce high mass halos (> 10 12 M ) and underproduce lower mass halos.…”

“…This feature had already been identified 5 in earlier numerical work on PNG. This interesting feature of non-Gaussianities may be particularly relevant in the context of the idea to solve the S 8 tension with non-linear effects [56]. In that case, the models NG1+ (with negative f NL ) and NG2-are the most interesting to investigate.…”

Full-shape BOSS constraints on dark matter interacting with dark radiation and lifting the S8 tension

“…First, the Hubble constant H 0 determined from the local distance ladder [1] and inferred indirectly within ΛCDM from the cosmic microwave background (CMB) anisotropies [2] as well as the scale of baryon acoustic oscillations (BAO) [3] disagree at a level of around 4σ (see [4,5] for reviews and [6,7] for summaries of proposed solutions). Second, the value of S 8 = σ 8 (Ω m /0.3) 0.5 , with σ 8 being the amplitude of matter clustering on a scale of 8 Mpc/h and Ω m the matter density parameter, measured from a variety of large-scale structure (LSS) probes (including weak lensing [8][9][10][11], galaxy cluster counts [12,13], and lensing combined with galaxy clustering [14]) are systematically below the value inferred from CMB measurements within ΛCDM, with a significance of up to 3σ (see also [15,16]). Third, the so-called small-scale crisis poses an intriguing puzzle [17,18].…”

On the consistency of $Λ$CDM with CMB measurements in light of the latest Planck, ACT, and SPT data

“…The most notable example is the 5𝜎 discrepancy in the value of the Hubble ★ E-mail: calderon@kasi.re.kr constant 𝐻 0 , as measured by low-𝑧 probes using the distance ladder Riess et al (2022) and high-𝑧 estimations, assuming ΛCDM. A milder (∼ 2𝜎) but longstanding discrepancy has also been reported between high and low-redshift estimations of the amplitude of matter fluctuations-characterized by 𝑆 8 ≡ 𝜎 8,0 √︁ Ω m,0 /0.3-the latter preferring lower values compared to the early universe predictions (Hikage et al 2019;Asgari et al 2020;Heymans et al 2021;Abbott et al 2022;Amon & Efstathiou 2022). The ΛCDM model is also facing other (less-relevant) observational challenges, see e.g.…”