Exclusive Chromomagnetism in heavy-to-light FCNCs

Abstract

We compute matrix elements of the chromomagnetic operator, often denoted by ${\mathcal{O}}_8$, between $B/D$-states and light mesons plus an off-shell photon by employing the method of light-cone sum rules (LCSR) at leading twist-2. These matrix elements are relevant for processes such as $B\to K^{\ast }{l}^{+}{l}^{-}$ and they can be seen as the analogues of the well-known penguin form factors $T_{1,2,3}$ and $f_T$. We find a large CP-even phase for which we give a long-distance (LD) interpretation. We compare our results to QCD factorisation for which the spectator photon emission is end-point divergent. The analytic structure of the correlation function used in our method admits a complex anomalous threshold on the physical sheet. The meaning and handling within the sum rule approach of the anomalous threshold is discussed.

Comments: 55 pages, 11 figures, nearly identical to published version in PRD