Detecting Axion-like Dark Matter with Linearly Polarized Pulsar Light

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.

Comments: 6 pages, 1 figure; calculation corrected, main conclusions unchanged, references added