# Detecting Axion-like Dark Matter with Linearly Polarized Pulsar Light

## TL;DR

This paper proposes using linearly polarized pulsar light to detect axion-like dark matter through birefringence effects, potentially probing very weak axion-photon couplings across a range of axion masses.

## Contribution

It introduces a novel observational method utilizing pulsar polarization to detect axion-like particles, extending current experimental limits.

## Key findings

- Potential to probe axion-photon coupling as small as 10^{-13} GeV^{-1}
- Can improve exclusion limits beyond CAST and SN1987A for certain axion masses
- Effective for axion masses between 10^{-22} and 10^{-19} eV

## Abstract

Non-relativistic QCD axions or axion-like particles are among the most popular candidates for cold Dark Matter (DM) in the universe. We proposed to detect axion-like DM, using linearly polarized pulsar light as a probe. Because of birefringence effect potentially caused by an oscillating galactic axion DM background, when pulsar light travels across the galaxy, its linear polarization angle may vary with time. With a soliton+NFW galactic DM density profile, we show that this strategy can potentially probe an axion-photon coupling as small as $\sim 10^{-13}$ GeV$^{-1}$ for axion mass $m_a \sim 10^{-22}-10^{-20}$ eV, given the current measurement accuracy. An exclusion limit stronger than CAST ($ \sim 10^{-10}$ GeV$^{-1}$) and SN1987A ($ \sim 10^{-11}$ GeV$^{-1}$) could be extended up to $m_a \sim 10^{-18}$ eV and $\sim 10^{-19}$ eV, respectively.