A Way Forward for Cosmic Shear: Monte-Carlo Control Loops

TL;DR

This paper proposes a novel calibration method for cosmic shear measurements using Monte Carlo control loops, aiming to reduce systematic errors and improve the reliability of weak lensing as a cosmological probe.

Contribution

It introduces a Monte Carlo control loop framework for calibrating cosmic shear measurements, drawing from particle physics and engineering techniques.

Findings

Control loops improve calibration robustness against systematics

Fast image simulations match statistical properties of real data

Method enhances the potential of cosmic shear for cosmology

Abstract

Weak lensing by large scale structure or 'cosmic shear' is a potentially powerful cosmological probe to shed new light on Dark Matter, Dark Energy and Modified Gravity. It is based on the weak distortions induced by large-scale structures on the observed shapes of distant galaxies through gravitational lensing. While the potentials of this purely gravitational effect are great, results from this technique have been hampered because the measurement of this weak effect is difficult and limited by systematics effects. In particular, a demanding step is the measurement of the weak lensing shear from wide field CCD images of galaxies. We describe the origin of the problem and propose a way forward for cosmic shear. Our proposed approach is based on Monte-Carlo Control Loops and draws upon methods widely used in particle physics and engineering. We describe the control loop scheme and show how it provides a calibration method based on fast image simulations tuned to reproduce the statistical properties of a specific cosmic shear data set. Through a series of iterative loops and diagnostic tests, the Monte Carlo image simulations are made robust to perturbations on modeling input parameters and thus to systematic effects. We discuss how this approach can make the problem tractable and unleash to full potential of cosmic shear for cosmology.