Muonium fine structure: theory update, tests of Lorentz violation, and experimental prospects Philipp Blumer, Svenja Geissmann, Arnaldo J. Vargas, Gianluca Janka, Ben Ohayon and Paolo Crivelli Eur. Phys. J. D, 79 3 (2025) 24 Published online: 26 March 2025 DOI: 10.1140/epjd/s10053-025-00971-6