A Strategy to Minimize Dust Foregrounds in B-mode Searches

TL;DR

This paper proposes a two-step observational strategy using high-frequency mapping to identify the cleanest sky patches for B-mode polarization searches, significantly enhancing sensitivity to primordial gravitational waves.

Contribution

It introduces an efficient method combining initial high-frequency mapping with subsequent low-frequency B-mode searches to minimize dust foreground contamination.

Findings

A ground-based 3-month experiment at >220 GHz can identify low-dust patches.

A balloon experiment at ~350 GHz can achieve similar results in less than two weeks.

This strategy can improve B-mode sensitivity by a factor of 2 to 3.

Abstract

The Planck satellite has identified several patches of sky with low polarized dust emission, obvious targets for searches for the cosmic-microwave-background (CMB) B-mode signal from inflationary gravitational waves. Still, given the Planck measurement uncertainties, the polarized dust foregrounds in these different candidate patches may differ by an order of magnitude or more. Here we show that a brief initial experiment to map these candidate patches more deeply at a single high frequency can efficiently zero in on the cleanest patch(es) and thus improve significantly the sensitivity of subsequent B-mode searches. A ground-based experiment with current detector technology operating at >~220 GHz for 3 months can efficiently identify a low-dust-amplitude patch and thus improve by up to a factor 2 or 3 on the sensitivity to cosmic B modes of the subsequent lower-frequency deep integration. A balloon experiment with current detector sensitivities covering the set of patches and operating at ~350 GHz can reach a similar result in less than two weeks. This strategy may prove crucial in accessing the smallest gravitational-wave signals possible in large-field inflation. The high-frequency data from this exploratory experiment should also provide valuable foreground templates to subsequent experiments that integrate on any of the candidate patches explored.