We compute matrix elements of the chromomagnetic operator, often denoted by 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 → K * 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. 1 md1e10@soton.ac.uk 2 J.D.Lyon@sms.ed.ac.uk 3 Roman.Zwicky@ed.ac.uk

We compute the isospin asymmetries in B → (K * , ρ)γ and B → (K, K * , ρ)l + l − for low lepton pair invariant mass q 2 , within the Standard Model (SM) and beyond the SM (BSM) in a generic dimension six operator basis. Within the SM the CPaveraged isospin asymmetries for B → (K, K * , ρ)ll, between 1 GeV 2 ≤ q 2 ≤ 4m 2 c , are predicted to be small (below 1.5%) though with significant cancellation. In the SM the non-CP averaged asymmetries for B → ρll deviate by ≈ ±5% from the CP-averaged ones. We provide physical arguments, based on resonances, of why isospin asymmetries have to decrease for large q 2 (towards the endpoint). Two types of isospin violating effects are computed: ultraviolet (UV) isospin violation due to differences between operators coupling to up and down quarks, and infrared (IR) isospin violation where a photon is emitted from the spectator quark and is hence proportional to the difference between the up-and down-quark charges. These isospin violating processes may be subdivided into weak annihilation (WA), quark loop spectator scattering (QLSS) and a chromomagnetic contribution. Furthermore we discuss generic selection rules based on parity and angular momentum for the B → Kll transition as well as specific selection rules valid for WA at leading order in the strong coupling constant. We clarify that the relation between the K and the longitudinal part of the K * only holds for leading twist and for left-handed currents. In general the B → ρll and B → K * ll isospin asymmetries are structurally different yet the closeness of α CKM to ninety degrees allows us to construct a (quasi) null test for the SM out of the respective isospin symmetries. We provide and discuss an update on B(B 0 → K * 0 γ)/B(B s → φγ) which is sensitive to WA.

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