Simulated forecasts for primordial B-mode searches in ground-based experiments

TL;DR

This paper assesses the challenges ground-based CMB experiments face in detecting primordial B-modes, focusing on foreground contamination and atmospheric noise, and provides forecasts for future experiment sensitivities.

Contribution

It introduces a Bayesian foreground cleaning method for simulated sky maps, accounting for foreground uncertainties and biases in measuring the tensor-to-scalar ratio r.

Findings

S3 experiments can constrain r to about 0.005-0.01

S4 experiments can constrain r to about 0.0005-0.001

A 2% polarized anomalous dust emission would be detectable by S4

Abstract

Detecting the imprint of inflationary gravitational waves on the $B$-mode polarization of the Cosmic Microwave Background (CMB) is one of the main science cases for current and next-generation CMB experiments. In this work we explore some of the challenges that ground-based facilities will have to face in order to carry out this measurement in the presence of Galactic foregrounds and correlated atmospheric noise. We present forecasts for Stage-3 (S3) and planned Stage-4 (S4) experiments based on the analysis of simulated sky maps using a map-based Bayesian foreground cleaning method. Our results thus consistently propagate the uncertainties on foreground parameters such as spatially-varying spectral indices, as well as the bias on the measured tensor-to-scalar ratio $r$ caused by an incorrect modelling of the foregrounds. We find that S3 and S4-like experiments should be able to put constraints on $r$ of the order $\sigma(r)=(0.5-1.0)\times10^{-2}$ and $\sigma(r)=(0.5-1.0)\times10^{-3}$ respectively, assuming instrumental systematic effects are under control. We further study deviations from the fiducial foreground model, finding that, while the effects of a second polarized dust component would be minimal on both S3 and S4, a 2\% polarized anomalous dust emission (AME) component would be clearly detectable by Stage-4 experiments.