### Abstract

We construct the gauge invariant three-photon decay amplitude of particle-antiparticle bound states modeled by the Dyson-Schwinger and Bethe-Salpeter equations. Application to the quark-antiquark (qq¯) bound states is emphasized. An essential aspect of our formulation is that it applies to any underlying quantum field theoretic model of the qq¯ system, and not just to models, like exact QCD, where the quark self-energy Σ couples to the electromagnetic field solely via dressed quark propagators. In this way, applications to effective field theories and other QCD motivated models are envisioned. The three-photon decay amplitude is constructed by attaching currents to all possible places in the Feynman diagrams contributing to the dressed quark propagator. The gauge invariance of our construction is thus a direct consequence of respecting the underlying structure of the quantum field theory determining the dynamics. In the resultant expression for the three-photon decay amplitude, all the basic ingredients consisting of the bound-state wave function, the final-state interaction qq¯ t matrix, the dressed quark propagator, and dressed quark currents, are determined by a universal Bethe-Salpeter kernel.

Original language | English |
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Article number | 045032 |

Pages (from-to) | 045032-1-045032-20 |

Number of pages | 20 |

Journal | Physical Review D |

Volume | 92 |

Issue number | 4 |

DOIs | |

Publication status | Published - 2015 |

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## Cite this

*Physical Review D*,

*92*(4), 045032-1-045032-20. [045032]. https://doi.org/10.1103/PhysRevD.92.045032