Cosmic microwave background constraints on the tensor-to-scalar ratio

TL;DR

This paper forecasts how accurately the Planck mission can measure the tensor-to-scalar ratio $r$ by considering realistic reionization histories and cut-sky effects, improving constraints on inflation models.

Contribution

It introduces an N-point interpolation method for reionization history to reduce bias in $r$ estimation and accounts for cut-sky effects in forecasts.

Findings

Bias from instantaneous reionization assumption is mitigated.

Constraints on $r$ within 5% error if true $r$ > 0.1.

Method improves accuracy of $r$ measurement in CMB data.

Abstract

One of the main goals of modern cosmic microwave background (CMB) missions is to measure the tensor-to-scalar ratio $r$ accurately to constrain inflation models. Due to ignorance about the reionization history $X_{e}(z)$, this analysis is usually done by assuming an instantaneous reionization $X_{e}(z)$ which, however, can bias the best-fit value of $r$. Moreover, due to the strong mixing of B-mode and E-mode polarizations in cut-sky measurements, multiplying the sky coverage fraction $f_{sky}$ by the full-sky likelihood would not give satisfactory results. In this work, we forecast constraints on $r$ for the Planck mission taking into account the general reionization scenario and cut-sky effects. Our results show that by applying an N-point interpolation analysis to the reionization history, the bias induced by the assumption of instantaneous reionization is removed and the value of $r$ is constrained within $5\%$ error level, if the true value of $r$ is greater than about 0.1 .