Accurate relativistic observables from postprocessing light cone catalogs

Abstract

We introduce and study a new scheme to construct relativistic observables from postprocessing light cone data. This construction is based on a novel approach, LC-metric, which takes general light cone or snapshot output generated by arbitrary N-body simulations or emulations and solves the linearized Einstein equations to determine the spacetime metric on the light cone. We find that this scheme is able to determine the metric to high precision, and subsequently generate accurate mock cosmological observations sensitive to effects such as post-Born lensing and nonlinear integrated Sachs-Wolfe contributions. By comparing to conventional methods in quantifying those general relativistic effects, we show that this scheme is able to accurately construct the lensing convergence signal. We also find that the accuracy of this method in quantifying the integrated Sachs-Wolfe effects in the highly nonlinear regime outperforms conventional methods by an order of magnitude. Furthermore, this scheme opens a new path for exploring and modeling higher-order and nonlinear general relativistic contributions to cosmological observables, including mock observations of gravitational lensing and the moving lens and Rees-Sciama effects.