Isospin Structure of Penguin Diagrams and Their Consequences in B Meson Physics

Isospin structure of electroweak penguin diagrams is different from the gluon-mediated or strong penguin. Given the large top mass, these electroweak contributions are significant. This has the consequence that some previous analyses which relied on a simple isospin structure in charmless B meson decays become inapplicable. We present the general Hamiltonian in next-to-leading order QCD, and illustrate our conclusion quantitatively for B-->ππ and B-->Kπ decays in the factorization approximation. Some remarks on CP asymmetries in B meson decays are also made.