Delensing for Precision Cosmology: Optimizing Future CMB B-mode Surveys to Constrain r

TL;DR

This paper develops an optimized delensing pipeline for future CMB B-mode surveys, combining CMB polarization data with large-scale structure tracers to improve constraints on the inflationary parameter r by reducing lensing contamination.

Contribution

It introduces a novel delensing framework that minimizes foreground bias, utilizes external LSS data, and demonstrates significant improvements in constraining r for ground-based CMB experiments.

Findings

Achieves 40% reduction in r uncertainty with CMB data alone.

Improves to 60% reduction when including LSS tracers.

Validates results with multiple likelihood methods.

Abstract

The detection of primordial B-modes, a key probe of cosmic inflation, is increasingly challenged by contamination from weak gravitational lensing B-modes induced by large-scale structure (LSS). We present a delensing pipeline designed to enhance the sensitivity to the inflationary parameter r, minimizing reliance on foreground mitigation during lensing reconstruction. Using simulations of Simons Observatory-like CMB observations and Euclid-like LSS surveys in the Northern hemisphere, we demonstrate that excluding low-l modes (l<200) effectively mitigates foreground biases, enabling robust lensing potential reconstruction using observed CMB polarization maps. We reconstruct the lensing potential with a minimum-variance (MV) quadratic estimator (QE) applied to CMB polarization data and combine this with external LSS tracers to improve delensing efficiency. Two complementary methods, the Gradient-order template and the Inverse-lensing approach, are used to generate lensing B-mode templates, which are cross-correlated with observed B-modes. This achieves a 40 percent reduction in the uncertainty of r with CMB-only reconstruction, improving to 60 percent when incorporating external LSS tracers. We validate our results using both the Hamimeche and Lewis likelihood and a Gaussian approximation, finding consistent constraints on r. Our work establishes a streamlined framework for ground-based CMB experiments, demonstrating that synergies with LSS surveys significantly enhance sensitivity to primordial gravitational waves.