Theoretical prediction for the muonium hyperfine-structure interval and its accuracy

Because there are new projects on the determination of the hyperfine interval in the ground state of muonium, we revisit different approaches to constructing its theoretical prediction and comparison with experimental data. We discuss a controversy in the accuracy of two recent predictions [Mohr et al., Rev. Mod. Phys. 88, 035009 (2016), and Eides, Phys. Lett. B 795, 113 (2019)] and produce a constraint on possible systematic errors in the determination of the muonium hyperfine-structure interval interval theoretically or experimentally. In particular, a possible additional theoretical term, that may be either a missing "regular" theoretical contribution or a contribution due to new physics, is estimated as -0.14(52) kHz. The constraint is based on all available data through a least-squares-adjustment procedure, including all their correlations. The result is close to the one of Eides [Phys. Lett. B 795, 113 (2019)].