TTP14-005 Hyperfine splitting in positronium to O(al^7 m_e): one-photon annihilation contribution

TTP14-005 Hyperfine splitting in positronium to O(al7 m_e): one-photon annihilation contribution
M. Baker, P. Marquard, A.A. Penin, J.H. Piclum, M. Steinhauser
Phys.Rev.Lett. 112 120407 2014
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