AI Insight
This paper examines the S8 tension in cosmology, a discrepancy between the amplitude of matter fluctuations (sigma_8) measured at low redshifts through cluster abundances, gravitational lensing, and redshift space distortions, versus the higher values predicted by the standard Lambda-CDM model from CMB data. The authors analyze sigma_8 redshift dependence using gauge-invariant formalism and argue that Einstein-Cartan cosmology, which incorporates spacetime torsion, naturally predicts higher mass density and sigma_8 at high redshifts, making the observed tension an expected outcome rather than an anomaly. The framework is also presented as potentially addressing related discrepancies highlighted by ALMA and JWST observations of early structure formation.
Why it matters
If Einstein-Cartan cosmology can consistently resolve the S8 tension and the anomalously early galaxy formation observed by JWST, it would represent a significant challenge to the standard Lambda-CDM model and motivate a fundamental revision of our understanding of cosmological structure formation.
arXiv:2502.20425v4 Announce Type: replace
Abstract: The measurements of cluster abundances, gravitational lensings, redshift space distortions and peculiar velocities at lower redshifts point out to much smaller sigma_8 than its value deduced from the measurements of the CMB fluctuations assuming the standard LCDM cosmology. High redshift measurements of ALMA and JWST imply even more striking problems for LCDM. We examine and compare the sigma_8 redshift dependence calculated within the gauge invariant formalism. Because the CMB fluctuations comprise a cosmological data from the recombination era to the present, the S_8 problem of the LCDM cosmology is not a surprise from the standpoint of the Einstein-Cartan cosmology because it predicts much larger mass density and sigma_8(z) than the LCDM model at high redshifts.