We present a phenomenological constraint on a pseudovector light boson beyond the Standard Model, which can induce a long-range spin-dependent interaction $\alpha^{ \prime\prime}({ \bf s}_1\cdot{ \bf s}_2)\,{ \rm e}^{ -\lambda r}/r$. In the range of masses from $4\;{ \rm keV}/c^2$ to those related to macroscopic distances (of $\lambda^{ -1}\sim1\;$cm) the spin-dependent coupling constant $\alpha^{ \prime\prime}$ of the electron-muon interaction is constrained at the level below a part in $10^{ 15}$. The constraint is weakened while extending to higher masses. The strongest constraint is related to the lepton-lepton interaction. Constraints on spin-dependent interactions of some other particles are also discussed. The results are obtained from data on the HFS interval of the ground state in muonium and a few other light hydrogen-like atoms.
Categories: hep-ph physics.atom-ph