The Superhorizon Test of Future B-mode Experiments

TL;DR

This paper discusses how future CMB polarization experiments can detect the superhorizon B-mode polarization signature predicted by inflation, distinguishing it from causal sources, and addresses measurement challenges and noise correction methods.

Contribution

It provides a detailed analysis of the superhorizon B-mode signature, methods to correct for experimental effects, and forecasts for future detection prospects.

Findings

Finite resolution causes spurious superhorizon power

Correction methods can mitigate data filtering effects

Forecasts show potential for detecting inflationary signals

Abstract

Inflation predicts B-mode polarization with correlations that span superhorizon scales at recombination. In contrast, the correlations set up by causal sources, such as phase transitions or defects, necessarily vanish on superhorizon scales. Motivated by BICEP2's B-mode detection, we consider the prospects for measuring the inflationary superhorizon signature in future observations. We explain that the finite resolution of an experiment and the filtering of the raw data induces a transfer of spurious subhorizon power to superhorizon scales, and describe ways to correct for it. We also provide a detailed treatment of possible sources of noise in the measurement. Finally, we present forecasts for the detectability of the signal with future CMB polarization experiments.