Searching for GUT-scale QCD Axions and Monopoles with a High-Voltage Capacitor*

The QCD axion has been postulated to exist because it solves the strong CP problem. Furthermore, if it exists axions should be created in the early Universe and could account for all the observed dark matter. In particular, axion masses of order 10^-10 to 10^-7 eV correspond to axions in the vicinity of the GUT-scale. In this mass range, many experiments have been proposed to search for the axion through the standard QED coupling parameter g_aγγ. Recently axion electrodynamics has been expanded to include two more coupling parameters, g_aEM and g_aMM, which could arise if heavy magnetic monopoles exist [1,2]. In this work, we show that both g_aMM and g_aEM may be searched for using a high-voltage capacitor [3]. Since the experiment is not sensitive to g_aγγ, it gives a new way to search for the effects of heavy monopoles if the GUT-scale axion is shown to exist or to simultaneously search for both the axion and the monopole at the same time.

[1] Anton V. Sokolov and Andreas Ringwald, Electromagnetic couplings of axions, arXiv:2205.02605, 2023.

[2] Anton V. Sokolov and Andreas Ringwald, Generic axion Maxwell equations: Path integral approach, arXiv:2303.10170, 2023.

[3] ME Tobar, AV Sokolov, A Ringwald, M Goryachev, “Searching for GUT-scale QCD axions and monopoles with a high-voltage capacitor,” Phys. Rev. D 108, 035024, 2023.