Evidence for deviation in gravitational light deflection from general relativity at cosmological scales with KiDS-Legacy and CMB lensing

TL;DR

This study tests general relativity at cosmological scales by combining multiple datasets, finding a significant deviation in gravitational light deflection that may indicate new physics or data issues.

Contribution

It provides the first combined analysis showing a deviation in gravitational light deflection from GR at cosmological scales using KiDS-Legacy and CMB lensing data.

Findings

KiDS-Legacy improves constraints on gravity parameters by up to 60%.

Gravitational light deflection deviation from GR is at 3.0σ in ΛCDM.

Deviation persists at 2.2σ in w0waCDM background.

Abstract

General relativity (GR) faces challenges from cosmic acceleration and observational tensions, necessitating stringent tests at cosmological scales. In this work, we probe GR deviations via a $\mu$--$\Sigma$ modified gravity parameterization, integrating KiDS-Legacy weak lensing (WL) data (1347 deg$^2$, $z\leq 2.0$), joint cosmic microwave background (CMB) data from Planck, ACT, and SPT, DESI DR2 baryon acoustic oscillation, and DES-Dovekie supernova data. KiDS-Legacy significantly improves constraint precision: $\mu_0$ (matter clustering) by $\sim 60\%$ and $\Sigma_0$ (gravitational light deflection) by $\sim 43\%$ relative to CMB alone. In the $\Lambda$CDM background, $\mu_0 = 0.21\pm 0.21$ is consistent with GR, while $\Sigma_0 = 0.149\pm 0.051$ deviates from GR at the 3.0$\sigma$ level. Furthermore, within the observationally preferred $w_0w_a$CDM background, this deviation in gravitational light deflection persists at the 2.2$\sigma$ level. This deviation is likely driven by the higher amplitudes in the large-scale CMB lensing measurements. This precise separation of GR-consistent matter clustering and deviant light deflection provides key observational clues for new physics or data systematics. Our work underscores the critical role of synergizing high-precision CMB and WL data in advancing GR tests.