---
author:
- |
    Yuval Grossman and Matthias Neubert[^1]\
    Stanford Linear Accelerator Center, Stanford University\
    Stanford, California 94309, U.S.A.\
    E-mail: ,
- |
    Alexander L. Kagan\
    Department of Physics, University of Cincinnati\
    Cincinnati, Ohio 45221, U.S.A.\
    E-mail:
title: Trojan Penguins and Isospin Violation in Hadronic B Decays
---

Introduction
============

The study of rare decay processes is an important tool in testing the fundamental interactions among elementary particles, exploring the origin of CP violation, and searching for New Physics beyond the Standard Model (SM). Such processes have been explored in great detail, both theoretically and in experimental searches, in the weak interactions of kaons and $B$ mesons, as well as in $K$–$\bar K$, $D$–$\bar D$, and $B$–$\bar B$ mixing. Two prominent examples are the evidence for mixing-induced CP violating in the decay $B\to J/\psi\,K_S$ reported by the CDF Collaboration [@CDF], and the observation of direct CP violation in the decays $K\to\pi\pi$ [@NA31; @E731], which has recently been confirmed by the KTeV and NA48 Collaborations [@KTeV; @NA48].

Flavor-changing neutral current (FCNC) processes, which are forbidden at tree level in the SM, are especially sensitive to any new source of flavor-violating interactions. Already, the absence of experimental signals for new FCNC couplings 