The Quest for B Modes from Inflationary Gravitational Waves

TL;DR

This paper reviews the theoretical background and experimental challenges in detecting B modes in the CMB polarization caused by inflationary gravitational waves, highlighting methods to distinguish them from other sources.

Contribution

It provides a comprehensive overview of the origin, polarization patterns, and detection strategies for inflationary gravitational waves in the CMB.

Findings

Inflationary gravitational waves produce distinctive B mode polarization.

Lensing and foregrounds can mimic B modes but are distinguishable.

Current strategies focus on isolating primordial B modes from other signals.

Abstract

The search for the curl component (B mode) in the cosmic microwave background (CMB) polarization induced by inflationary gravitational waves is described. The canonical single-field slow-roll model of inflation is presented, and we explain the quantum production of primordial density perturbations and gravitational waves. It is shown how these gravitational waves then give rise to polarization in the CMB. We then describe the geometric decomposition of the CMB polarization pattern into a curl-free component (E mode) and curl component (B mode) and show explicitly that gravitational waves induce B modes. We discuss the B modes induced by gravitational lensing and by Galactic foregrounds and show how both are distinguished from those induced by inflationary gravitational waves. Issues involved in the experimental pursuit of these B modes are described, and we summarize some of the strategies being pursued. We close with a brief discussion of some other avenues toward detecting/characterizing the inflationary gravitational-wave background.