Structure-dependent QED effects in exclusive <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>B</mml:mi></mml:math> decays at subleading power
Claudia Cornella, Matthias König, Matthias Neubert
Abstract
We derive a factorization theorem for the structure-dependent QED effects in the weak exclusive process ${B}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$, i.e., effects probing the internal structure of the $B$ meson. The derivation requires a careful treatment of end-point-divergent convolutions common to subleading-power factorization formulas. We find that the decay amplitude is sensitive to two- and three-particle light-cone distribution amplitudes of the $B$ meson as well as to a new hadronic quantity $F(\ensuremath{\mu},\mathrm{\ensuremath{\Lambda}})$, which generalizes the notion of the $B$-meson decay constant in the presence of QED effects. This is one of the first derivations of a subleading-power factorization theorem in which the soft functions are nonperturbative hadronic matrix elements.