Upper limit on the axion-photon coupling from magnetic white dwarf polarization

Abstract

Polarization measurements of thermal radiation from magnetic white dwarf (MWD) stars have been proposed as a probe of axion-photon mixing. The radiation leaving the surface of the MWD is unpolarized, but if low-mass axions exist then photons polarized parallel to the direction of the MWD's magnetic field may convert into axions, which induces a linear polarization dependent on the strength of the axion-photon coupling $g_{a\gamma \gamma }$. We model this process by using the formalism of axion-photon mixing in the presence of strong-field vacuum birefringence to show that of all stellar types MWDs are the most promising targets for axion-induced polarization searches. We then consider linear polarization data from multiple MWDs, including SDSS J135141 and Grw+70${}^{\circ }$8247, to show that after rigorously accounting for astrophysical uncertainties the axion-photon coupling is constrained to $|g_{a\gamma \gamma }|\lesssim 5.4\times 10^{-12}$ GeV${}^{-1}$ at 95% confidence for axion masses $m_a\lesssim 3\times 10^{-7}$ eV. This upper limit puts in tension the previously-suggested explanation of the anomalous transparency of the Universe to TeV gamma-rays in terms of axions. We identify MWD targets for which future data and modeling efforts could further improve the sensitivity to axions.

22 pages, 9 figures

References in corpus (10)

• Revisiting the bound on axion-photon coupling from Globular Clusters
• Revisiting the SN1987A gamma-ray limit on ultralight axion-like particles
• On the Spectral Evolution of Hot White Dwarf Stars. I. A Detailed Model-Atmosphere Analysis of Hot White Dwarfs from SDSS DR12
• Lower limit on the strength and filling factor of extragalactic magnetic fields
• Simulations of extragalactic magnetic fields and of their observables
• A highly magnetised and rapidly rotating white dwarf as small as the Moon
• Probing Axions with Radiation from Magnetic Stars
• The long term polarimetric variability of the strongly magnetic white dwarf Grw+70${}^{\circ }$8247
• Photon-ALP interaction as a measure of initial photon polarization
• How do Magnetic Field Models Affect Astrophysical Limits on Light Axion-like Particles? An X-ray Case Study with NGC 1275