Inference of $B$-mode polarization in the presence of non-Gaussian foregrounds

TL;DR

This paper develops methods to accurately infer primordial gravitational wave signals in CMB polarization data, accounting for complex foreground contamination and spatial variations, crucial for future high-precision cosmological observations.

Contribution

It introduces a combined approach using cMILC and power-spectrum methods to separate and analyze B-mode signals amidst non-Gaussian foregrounds and varying spectral energy distributions.

Findings

Methods effectively remove foreground contamination in simulated data.

Detection prospects depend on foreground complexity and instrument sensitivity.

Validated techniques improve B-mode signal extraction for future experiments.

Abstract

The inflationary $B$-mode signals encode invaluable information about the origin of our Universe and searching for potential signatures of primordial gravitational waves (PGWs) is one of the major science goals for future precision observations of cosmic microwave background (CMB) polarization. However, dominant $B$-mode signals of both Galactic foreground contamination and gravitational lensing effects prevent direct measurements of the PGW $B$-mode signals. There are existing proposals which can effectively eliminate these two contaminants but issues remain for future high-sensitivity and multifrequency CMB polarization observations, such as spatially-varying spectral energy distribution (SED) of polarized foreground and cosmological $B$-mode signals due to primordial magnetic fields (PMFs). In this work, we investigate inference of PGW $B$-mode signals in the presence of both complexities. We employ a constrained moment internal linear combination (cMILC) method to remove polarization signals arising from spatially varying SEDs. Also, we employ a power-spectrum-based approach to extracting both the Galactic and cosmological $B$-mode components. Two methods have been validated by mock data and different consistency tests have been performed. We apply these two methods to end-to-end simulations for future high-sensitivity and multifrequency polarization observations and investigate the detectability of different $B$-mode signals in the presence of non-Gaussian polarized foregrounds under different scenarios. This study will be important for new physics studies with $B$-mode signatures.