Cosmic Polarization Rotation, Cosmological Models, and the Detectability of Primordial Gravitational Waves

TL;DR

This paper reviews how CMB polarization measurements can test fundamental physics, including pseudoscalar-photon interactions and primordial gravitational waves, with upcoming missions promising more precise insights into cosmology and particle physics.

Contribution

It provides a comprehensive review of how future CMB polarization observations can detect pseudoscalar-photon interactions and primordial gravitational waves, exploring their implications for fundamental physics.

Findings

Future missions will improve sensitivity to polarization rotations.

Potential detection of pseudoscalar-photon interactions indicating new physics.

Primordial gravitational waves may be directly detected by space GW detectors.

Abstract

CMB (Cosmic Microwave Background) polarization observations test many aspects of cosmological models. Effective pseudoscalar-photon interaction(s) would induce a rotation of linear polarization of electromagnetic wave propagating with cosmological distance in various cosmological models. CMB polarization observations are superb tests of these models and have the potential to discover new fundamental physics. Pseudoscalar-photon interaction is proportional to the gradient of the pseudoscalar field. From phenomenological point of view, this gradient could be neutrino number asymmetry, other density current, or a constant vector. In these situations, Lorentz invariance or CPT may effectively be violated. In this paper, we review these results and anticipate what more precise observations can tell us about fundamental physics, inflation, etc. Better accuracy in CMB polarization observation is expected from PLANCK mission to be launched this year. Dedicated CMB polarization observers like B-Pol mission, CMBpol mission and LiteBIRD mission would probe this fundamental issue more deeply in the future. With these sensitivities, cosmic polarization rotations from effective pseudoscalar-photon interaction, Faraday polarization rotations from primordial and large-scale magnetic field, and tensor modes effects would have chances to be detected and distinguished. The subtracted tensor-mode effects are likely due to primordial gravitational waves. We discuss the direct detectability of these primordial gravitational waves using space GW detectors.