# Exploration of the polarization angle variability of the Crab Nebula with POLARBEAR and its application to the search for axion-like particles

**Authors:** Shunsuke Adachi, Tylor Adkins, Carlo Baccigalupi, Yuji Chinone, Kevin T. Crowley, Josquin Errard, Giulio Fabbian, Chang Feng, Takuro Fujino, Masaya Hasegawa, Masashi Hazumi, Oliver Jeong, Daisuke Kaneko, Brian Keating, Akito Kusaka, Adrian T. Lee, Anto I. Lonappan, Yuto Minami, Masaaki Murata, Lucio Piccirillo  
**arXiv:** [2403.02096](https://arxiv.org/abs/2403.02096)  
**Date:** 2024-03-04  
**Summary page:** https://www.summarizepaper.com/en/paper/2403.02096v1/

## Key points

- The Crab Nebula, also known as Tau A, is a well-known polarized astronomical source at millimeter wavelengths.
- Recent studies have shown variability in both intensity and polarization of the Crab Nebula across different wavelengths.
- Studying this variability presents an opportunity to investigate the dynamics of Tau A and assess its reliability as a calibration standard.
- One application of studying this variability is in the search for axion-like particles (ALPs) which interact with photons through a Chern-Simons term.
- Researchers evaluated the polarization angle variability of the Crab Nebula using observations from 2015 and 2016 with the 150 GHz POLARBEAR instrument.
- The findings reveal a median 95% upper bound on the amplitude of polarization oscillation ($A < 0.065^\circ$) across frequencies ranging from $0.75~\mathrm{year}^{-1}$ to $0.66~\mathrm{hour}^{-1}$.
- This bound translates into a median 95% upper limit on ALP-photon coupling ($g_{a\gamma\gamma} < 2.16\times10^{-12}\,\mathrm{GeV}^{-1}\times(m_a/10^{-21} \mathrm{eV})$) within a specific mass range.
- Leveraging bright polarized sources like the Crab Nebula can be effective in constraining ALPs, similar to cosmic microwave background data.
- The study contributes valuable insights to understanding astrophysical processes and theoretical frameworks governing particle interactions at cosmological scales.

## Summary

The Crab Nebula, also known as Tau A, is a well-known polarized astronomical source at millimeter wavelengths. It has traditionally served as a stable light source for polarization angle calibration in millimeter-wave astronomy. Recent studies have shown that both its intensity and polarization exhibit variability over time across a range of wavelengths. This presents an intriguing opportunity to investigate the dynamics of Tau A and assess its reliability as a calibration standard. One particularly fascinating application of studying this variability is in the search for axion-like particles (ALPs). Ultralight ALPs interact with photons through a Chern-Simons term, leading to temporal oscillations in the polarization angle of linearly polarized sources. By meticulously analyzing systematic errors and ensuring internal consistency, researchers have evaluated the polarization angle variability of the Crab Nebula using observations from 2015 and 2016 conducted with the 150 GHz POLARBEAR instrument. The findings reveal a median 95% upper bound on the amplitude of polarization oscillation ($A < 0.065^\circ$) across frequencies ranging from $0.75~\mathrm{year}^{-1}$ to $0.66~\mathrm{hour}^{-1}$. Under the assumption that ALPs are solely responsible for Tau A's polarization angle variations, constitute all dark matter, and follow a stochastic Gaussian field distribution, this bound translates into a median 95% upper limit on ALP-photon coupling ($g_{a\gamma\gamma} < 2.16\times10^{-12}\,\mathrm{GeV}^{-1}\times(m_a/10^{-21} \mathrm{eV})$) within the mass range from $9.9\times10^{-23} \mathrm{eV}$ to $7.7\times10^{-19} \mathrm{eV}. These results demonstrate that leveraging bright polarized sources like the Crab Nebula can be just as effective as utilizing cosmic microwave background polarization data in constraining ALPs. Overall, this study not only sheds light on the intricate behavior of polarized astronomical sources but also underscores their potential significance in probing fundamental physics phenomena such as axion-like particles. The refined analysis presented here contributes valuable insights to our understanding of both astrophysical processes and theoretical frameworks governing particle interactions at cosmological scales.