Complete super-sample lensing covariance in the response approach

TL;DR

This paper derives a comprehensive model for super-sample covariance in weak lensing, incorporating tidal effects and beyond flat-sky approximations, crucial for accurate cosmic shear analysis.

Contribution

It introduces a complete super-sample covariance framework using the response approach, including tidal effects and general sky geometries, for improved lensing covariance modeling.

Findings

Super-sample covariance contributes about 10% under flat-sky and Limber approximations.

Tidal field contributions account for roughly 5% of the lensing covariance at high multipoles.

Including tidal and beyond approximations significantly impacts covariance estimates in cosmic shear studies.

Abstract

We derive the complete super-sample covariance (SSC) of the matter and weak lensing convergence power spectra using the power spectrum response formalism to accurately describe the coupling of super- to sub-survey modes. The SSC term is completely characterized by the survey window function, the nonlinear matter power spectrum and the full first-order nonlinear power spectrum response function, which describes the response to super-survey density and tidal field perturbations. Generalized separate universe simulations can efficiently measure these responses in the nonlinear regime of structure formation, which is necessary for lensing applications. We derive the lensing SSC formulae for two cases: one under the Limber and flat-sky approximations, and a more general one that goes beyond the Limber approximation in the super-survey mode and is valid for curved sky applications. Quantitatively, we find that for sky fractions $f_{\rm sky} \approx 0.3$ and a single source redshift at $z_S=1$, the use of the flat-sky and Limber approximation underestimates the total SSC contribution by $\approx 10\%$. The contribution from super-survey tidal fields to the lensing SSC, which has not been included in cosmological analyses so far, is shown to represent about $5\%$ of the total lensing covariance on multipoles $\ell_1,\ell_2 \gtrsim 300$. The SSC is the dominant off-diagonal contribution to the total lensing covariance, making it appropriate to include these tidal terms and beyond flat-sky/Limber corrections in cosmic shear analyses.