Using the Crab Nebula as a high precision calibrator for Cosmic Microwave Background polarimeters

TL;DR

This paper proposes using the Crab Nebula as a highly precise calibrator for CMB polarization measurements, aiming to improve the detection of inflationary B-modes and constrain fundamental physics.

Contribution

It introduces a method to measure Crab Nebula's polarization with 0.1° accuracy using Mars for calibration, enhancing CMB polarization calibration.

Findings

Crab Nebula polarization can be calibrated to 0.1° accuracy.

Improved calibration reduces false B-mode signals.

Enhanced measurements can constrain neutrino masses and exotic physics.

Abstract

The polarization of the Cosmic Microwave Background (CMB) provides a plethora of information about the early universe. Most notably, gravitational waves from the Inflationary epoch (the leading explanation of the origin of the universe) create a unique CMB polarization $B$-mode signal. An unambiguous detection of the inflationary $B$-mode signal would be a window into the physics of the universe as it was $10^{-36}$ seconds after the Big Bang, at energy scales many orders of magnitude larger than what the LHC can produce. However, there are several instrumental and astrophysical sources that can obfuscate the inflationary $B$-mode signal. One of the most difficult parameters to calibrate for CMB telescopes is the absolute orientation of the antenna's polarization sensitive axis. A miscalibration of the polarization orientation rotates the much brighter $E$-mode signal, producing a false $B$-mode signal. The current best uncertainty on polarization orientation in the CMB community is $0.5^\circ$, set from extrapolating IRAM measurements of the Crab Nebula supernova remnant at 90 GHz to 150 GHz, where the CMB signals peak. This accuracy is not sufficient to convincingly detect $B$-modes predicted by currently allowable models of Inflation. We suggest to precisely measure the Crab Nebula's polarization, which can be calibrated absolutely to $0.1^\circ$ from measurements of the polarized emission of Mars, and use these data to calibrate current and upcoming CMB experiments. In addition to inflationary $B$-modes, more precise calibration will allow us to better constrain the sum of the neutrino masses and set limits on exotic physics such as parity violation through cosmic polarization rotation.