Isospin breaking in B→K∗γ decays

A calculation of the leading isospin-breaking contributions to the B→K∗γ decay amplitudes based on the QCD factorization approach is presented. They arise at order Λ/mb in the heavy-quark expansion and are due to annihilation contributions from 4-quark operators, the chromo-magnetic dipole operator, and charm penguins. In the Standard Model the decay rate for B 0→K∗0γ is predicted to be about 10–20% larger than that for B−→K∗−γ. Isospin-breaking effects are a sensitive probe of the penguin sector of the effective weak Hamiltonian. New Physics models in which the hierarchy of B→K∗γ decay rates is either flipped or greatly enhanced could be ruled out with more precise data.