Hunting Axion Dark Matter with Protoplanetary Disk Polarimetry

We find that the polarimetric observations of protoplanetary disks are useful to search for ultralight axion dark matter. Axion dark matter predicts the rotation of the linear polarization plane of propagating light, and protoplanetary disks are ideal targets to observe it. We show that a recent observation puts the tightest constraint on the axion-photon coupling constant for an axion mass $m\lesssim {10}^{-21}\mathrm{eV}$.

Figure 1

(Top) Simulated polarization vectors of AB Aur at $\lambda =1.6\mu \mathrm{m}$. Red and white bars represent the direction of scattering polarization and perpendicular to the radial vectors, respectively. (Bottom) Histogram of polarization angles with respect to radial vectors. Black and red lines are the Gaussian fits of the histograms of simulated and observed values from Hashimoto et al. [31], respectively.

Figure 2

Constraint on the coupling constant $g_{a\gamma }$ for varying mass of the axion dark matter $m$. The black solid line indicates the upper bound derived in Eq. (14), whereas the gray solid line is the conservative upper bound. Blue, green, and red regions are rejected by the experiment (CAST [14]) and astronomical observations (SN 1987A [17] and Quasor polarization [18]). Black broken lines are the expected sensitivities of future projects (ALPS-II [16] and IAXO [15]) and red broken lines are presumptive lower limits from observations (soft x-ray [19] and $\gamma$-ray transparency [20]).