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We compute matrix elements of the chromomagnetic operator, often denoted by ${\cal O}_8$, between $B/D$-states and light mesons plus an off-shell photon byemploying the method of light-cone sum rules (LCSR) at leading twist-2. Thesematrix elements are relevant for processes such as $B \to K^* l^+l^-$ and theycan 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 thespectator photon emission is end-point divergent. The analytic structure of thecorrelation function used in our method admits a complex anomalous threshold onthe physical sheet. The meaning and handling within the sum rule approach ofthe anomalous threshold is discussed.

Exclusive Chromomagnetism in heavy-to-light FCNCs