Polarization Signals from Axion-Photon Resonant Conversion in Neutron Star Magnetosphere

Abstract

Neutron stars provide ideal astrophysical laboratories for probing new physics beyond the Standard Model. If axions exist, photons can develop linear polarization during photon-axion conversion in the magnetic field of a neutron star. We find that the plasma in the neutron star magnetosphere could dramatically enhance the polarization through the resonant conversion effect. With the polarization measurements from PSR B0656+14, 4U 0142+61, and the benchmark polarization measurement in the mid-infrared band, we demonstrate that optical and infrared polarization from neutron stars can provide strong constraints on the axion-photon coupling over a broad axion mass range $10^{-11}\lesssim m_a\lesssim 10^{-3}$ eV.

Comments: 7+5 pages, 2+2 figures.V2: matches published paper in PRD