Abstract
Isospin-breaking in B → ππ caused by π0 − η − η' mixing is studied in a model-independent way using flavor SU(3). Measured branching ratios for B+ → π+π0, B+ → π+η( ') and B0 → π0η( ') imply an uncertainty in α smaller than 1.4◦. We find a negligible effect of π0 − η − η' mixing on α in B → ρπ. Characterizing the effect of ρ0 − ω mixing in B → ρρ and in B → ρπ by the two-pion invariant mass dependence, we point out a way of constraining this effect experimentally or eliminating it altogether. We show that a model-independent shift in α caused by electroweak penguin amplitudes in B → ππ and B → ρρ, �αEWP = (1.5 ± 0.3)◦, may be slightly different in B → ρπ. Other sources of isospin-breaking in these processes are briefly discussed.