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arXiv · 0705.1330

The soft-energy region in the radiative decay of bound states

Pedro D. Ruiz-Femenia
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Abstract

The orthopositronium decay to three photons is studied in the phase-space region where one of the photons has an energy comparable to the relative three-momentum of the e+e- system (w ~ m alpha). The NRQED computation in this regime shows that the dominant contribution arises from distances ~ 1/(mw)^(1/2), which allows to treat the Coulomb interaction perturbatively. The small-photon energy expansion of the 1-loop decay spectrum from full QED yields the same result as the effective theory. By doing the threshold expansion of the 1-loop QED amplitude we confirm that the leading term arises from a loop-momentum region where q^0 ~ q^2/m ~ w. This corresponds to a new non-relativistic loop-momentum region, which has to be taken into account for the description of a non-relativistic particle-antiparticle system that decays through soft photon emission.

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Pedro D. Ruiz-Femenia. 2007-09-20. The soft-energy region in the radiative decay of bound states. https://doi.org/10.1016/j.nuclphysb.2007.07.013

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