= Radiative pion decay
{title2=$\pi^+\to\ell^+\nu_\ell\gamma$}
A charged <pion> decays to a charged <antilepton>, its associated <neutrino>, and a <photon>. Inner <bremsstrahlung> from charged external states interferes with structure-dependent radiation. An experimentally resolved <photon> needs an <energy> cut: the real-radiation rate alone diverges in the soft limit, whereas a suitably inclusive combination with virtual <radiative corrections> is finite.<Radiative pion and kaon decay form factors in the 2025 Review of Particle Physics>[Section 62.1, especially equations (62.1)–(62.4)]{ref}
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