Dark Energy Survey Year 3 Results: Cosmological constraints from second- and third-order shear statistics

We present a cosmological analysis of the third-order aperture mass statistic using Dark Energy Survey Year 3 (DES Y3) data. We perform a complete tomographic measurement of the three-point correlation function of the Y3 weak lensing shape catalog with the four fiducial source redshift bins. Building upon our companion methodology paper, we apply a pipeline that combines the two-point function ξ_± with the mass aperture skewness statistic <M³_ap>, which is an efficient compression of the full shear three-point function. We use a suite of simulated shear maps to obtain a joint covariance matrix. By jointly analyzing ξ_± and <M³_ap> measured from DES Y3 data with a ΛCDM model, we find S₈ = 0.780 ± 0.015 and Ω_m = 0.266⁺₋₀⁰_.^.₀₄₀ ⁰³⁹, yielding 111% of figure-of-merit improvement in the Ω_m-S₈ plane relative to ξ_± alone, consistent with expectations from simulated likelihood analyses. With a wCDM model, we find S₈ = 0.749⁺₋₀⁰_.^.₀₂₆ ⁰²⁷ and w₀ = −1.39 ± 0.31, which gives an improvement of 22% on the joint S₈-w₀ constraint. Our results are consistent with w₀ = −1. Our new constraints are compared to CMB data from the Planck satellite, and we find that with the inclusion of <M³_ap> the existing tension between the datasets is at the level of 2.3σ. We show that the third-order statistic enables us to self-calibrate the mean photometric redshift uncertainty parameter of the highest redshift bin with little degradation in the figure of merit. Our results demonstrate the constraining power of higher-order lensing statistics and establish <M³_ap> as a practical observable for joint analyses in current and future surveys.