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arXiv · 2504.12377

Search for Axions in Magnetic White Dwarf Polarization at Lick and Keck Observatories

Joshua N. Benabou·Christopher Dessert·Kishore C. Patra·Thomas G. Brink·WeiKang Zheng·Alexei V. Filippenko·Benjamin R. Safdi
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Abstract

We present the most sensitive search to date for light axion-like particles with masses below a micro-eV, using spectropolarimetric data collected from the Lick and Keck Observatories. The conversion of optical photons emitted from the surface of a magnetic white dwarf (MWD) into axions in the strong magnetic field around the star induces a nearly wavelength-independent linear polarization in the observed starlight. We analyze the Stokes parameters $(U, Q, I)$ measured with the Kast spectrograph at the Lick Observatory toward the MWDs SDSS J033320+000720 and ZTF J190132+145807, and with the LRISp-ADC instrument at the Keck Observatory toward ZTF J190132+145807, SDSS J002129+150223, and SDSS J100356+053825 to search for this effect. The data show no evidence of axion-induced linear polarization, and we set world-leading constraints on the axion-photon coupling $|g_{aγγ}| \lesssim 1.7 \times 10^{-12} \,\mathrm{GeV}^{-1}$ at the $95\%$ confidence level for masses $m_a \lesssim 2 \times 10^{-7}\,\mathrm{eV}$.

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Joshua N. Benabou, Christopher Dessert, Kishore C. Patra, Thomas G. Brink, WeiKang Zheng, Alexei V. Filippenko, Benjamin R. Safdi. 2025-04-16. Search for Axions in Magnetic White Dwarf Polarization at Lick and Keck Observatories. https://arxiv.org/abs/2504.12377

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