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Parapositronium decay into three photons and implications for the neutral pion

Andrzej Czarnecki*, Divyesh Dagia†, Ting Gao‡, and Ripanjeet Toor§

  • *Contact author: andrzejc@ualberta.ca
  • †Contact author: dagia@ualberta.ca
  • ‡Contact author: tgao7@ualberta.ca
  • §Contact author: ripanjee@ualberta.ca
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Phys. Rev. D 113, 073002 – Published 6 April, 2026

DOI: https://doi.org/10.1103/b6kd-v8xn

Abstract

We complete the determination of the parapositronium decay into three photons by evaluating amplitudes mediated by the Z boson. We show that, contrary to the expectation that the extra mass scale me may bring an enhancement to the overall scaling, the amplitude turns out to start at 1/mZ6 order, similarly to the W boson mediated amplitude. The decay rate with both W and Z boson contributions is found to be 1.1×10−80  eV, about 47 orders of magnitude smaller than previously estimated. We also discuss its implication for the π0→3γ amplitude.

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Phys. Rev. D 113, 073002– Published 6 April, 2026
  • Received 15 February 2026
  • Accepted 16 March 2026
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