Delensing Degree-Scale $B$-Mode Polarization with High-Redshift Line Intensity Mapping

TL;DR

This paper explores how high-redshift line intensity mapping can enhance the removal of lensing-induced B-mode polarization in CMB experiments, potentially improving delensing efficiency by about 11% if low-k modes are measured effectively.

Contribution

It demonstrates that tomographic line intensity mapping at high redshifts can significantly improve delensing performance for CMB B-mode measurements, contingent on low-k mode measurement capabilities.

Findings

High-redshift IM can improve delensing by ~11%.

Next-generation IM experiments can achieve the necessary sensitivity.

Measurement of low-k modes is crucial for effective delensing.

Abstract

Cosmic microwave background (CMB) experiments that constrain the tensor-to-scalar ratio $r$ are now approaching the sensitivity at which delensing---removing the $B$ modes induced by the gravitational lensing of large-scale structure---is necessary. We consider the improvement in delensing that maps of large-scale structure from tomographic line intensity mapping (IM) experiments targeting $2 < z < 10$ could provide. Compared to a nominal baseline of cosmic infrared background and internal delensing at CMB-S4 sensitivity, we find that the addition of high-redshift IM data could improve delensing performance by ~11%. Achieving the requisite sensitivity in the IM data is feasible with next-generation experiments that are now being planned. However, these results are contingent on the ability to measure low-$k$ modes along the line of sight. Without these modes, IM datasets are unable to to correlate with the lensing kernel and do not aid in delensing.