First Constraint on Axion-Photon Coupling $g_{\hat{I}}^3$ from Neutron Star Observations

Abstract

We propose a novel method to detect axions which uniquely depends on the dimensionless axion-photon coupling $g_{\hat{I}}^3$, independent of the suppressive axion decay constant $f_a$. Using neutron star PSR B1919+21 data from the Five-hundred-meter Aperture Spherical Telescope, we derive the first constraint $|g_{\hat{I}}^3|<0.93$ at $1\ddot{I}ƒ$ confidence level for ultra-light axions ($m_a<10^{-11}$ eV).

6 pages, 3 figures