First measurement of the Weyl potential evolution from the Year 3 Dark Energy Survey data: Localising the $σ_8$ tension

Abstract: We present the first measurement of the Weyl potential at four redshifts bins using data from the first three years of observations of the Dark Energy Survey (DES). The Weyl potential, which is the sum of the spatial and temporal distortions of the Universe's geometry, provides a direct way of testing the theory of gravity and the validity of the $\Lambda$CDM model. We find that the measured Weyl potential is 2.3$\sigma$, respectively 3.1$\sigma$, below the $\Lambda$CDM predictions in the two lowest redshift bins. We show that these low values of the Weyl potential are at the origin of the $\sigma_8$ tension between Cosmic Microwave Background (CMB) measurements and weak lensing measurements. Interestingly, we find that the tension remains if no information from the CMB is used. DES data on their own prefer a high value of the primordial fluctuations, followed by a slow evolution of the Weyl potential. A remarkable feature of our method is that the measurements of the Weyl potential are model-independent and can therefore be confronted with any theory of gravity, allowing efficient tests of models beyond General Relativity.

• The paper presents the first measurement of the Weyl potential evolution using DES Year 3 data to pinpoint the σ8 tension.
• It employs a model-independent methodology, revealing 2.3σ and 3.1σ deviations in the two lowest redshift bins from ΛCDM predictions.
• The results offer empirical constraints on alternative gravity models and set benchmarks for future surveys like Euclid and LSST.

First Measurement of the Weyl Potential Evolution from the Year 3 Dark Energy Survey Data: Localizing the $\sigma_8$ Tension

The paper presents a pivotal analysis in cosmology, offering the first measurement of the Weyl potential evolution using the Year 3 Dark Energy Survey (DES) data. Focusing on four redshift bins, the study explores both the practical measurement aspects and theoretical implications of the Weyl potential as a diagnostic tool for cosmic structure and potential deviations from the $\Lambda$CDM model.

Measurement Results and $\sigma_8$ Tension

The Weyl potential, being a linear combination of scalar gravitational potentials, offers a potent avenue for probing gravitation in cosmological structures. The findings reveal a statistically significant deviation from $\Lambda$CDM predictions, specifically in the two lowest redshift bins: 2.3$\sigma$ and 3.1$\sigma$ discrepancies are reported. This departure localizes the mysterious $\sigma_8$ tension, which pertains to differing measurements of cosmic structure growth as observed via Cosmic Microwave Background (CMB) versus large-scale structure surveys like DES.

A noteworthy aspect of this analysis is the methodology's independence from specific cosmological models. This model-independence allows the paper to make robust claims about potential deviations from standard cosmological understanding without being tied to particular theoretical frameworks.

Implications for Gravity Theories and Cosmological Models

The divergence in the Weyl potential evolution is contextualized in terms of its potential implications for theories beyond General Relativity (GR). Since the measurements are performed without relying on a specific cosmological model, they are amenable to testing against any gravitational theory that can be articulated at cosmological scales. Importantly, this analysis provides pivotal empirical constraints for alternative models of gravity, such as those expanding upon or revising the traditional $\Lambda$CDM framework.

Predictions for Future Surveys and Experiments

This paper's methodological approach and findings have critical implications for the anticipated data from forthcoming surveys such as Euclid and the Large Synoptic Survey Telescope (LSST). With predicted increased precision and broader sky coverage, these future surveys could potentially resolve current tensions and offer more exhaustive constraints on the Weyl potential, thereby refining our understanding of cosmic structure evolution.

Conclusion

In sum, this study not only challenges current assumptions within the standard cosmological model but also showcases an innovative, model-agnostic methodology for exploring the fundamental forces shaping our Universe. The implications of this work stretch across theoretical and experimental domains, setting a new benchmark for future investigations into the evolution of cosmic structures and the models governing them.