Hyperfine structure of excited state of muonic helium atom
  The recoil, vacuum polarization and electron vertex corrections of first and second orders in the fine structure constant $\alpha$ and the ratio of electron to muon and electron to \alpha-particle masses are calculated in the hyperfine splitting of the $1s^{(e)}_{1/2}2s^{(\mu)}_{1/2}$ state of muonic helium atom (\mu e ^4_2He) on the basis of a perturbation theory. We obtain total result for the muonically excited state hyperfine splitting $\Delta \nu^{hfs}=4295.66$ MHz which improves previous calculations due to the account of new corrections and more accurate treatment of the electron vertex contribution. 
A.A. Krutov (Samara State U.) and A.P. Martynenko (Samara State U. &   Samara State Aerospace U.)
hep-ph physics.atom-ph