LPN14-045 Hyperfine splitting in positronium to O(alpha^7 m_e): one-photon annihilation contribution

LPN14-045 Hyperfine splitting in positronium to O(alpha7 m_e): one-photon annihilation contribution
M. Baker, P. Marquard, A.A. Penin, J. Piclum, M. Steinhauser
Phys.Rev.Lett. 112 120407 2014
arXiv