O(alpha^3 ln alpha) corrections to muonium and positronium hyperfine   splitting
  We compute O(alpha^3 ln alpha) relative corrections to the ground state hyperfine splitting of a QED two body bound state with different masses of constituents. The general result is then applied to muonium and positronium. In particular, a new value of the muon to electron mass ratio is derived from the muonium ground state hyperfine splitting. 
Kirill Melnikov and Alexander Yelkhovsky