Charmless Final State Interaction in B-> pi pi decays
  We estimate effects of the final state interactions in B -> pi pi decays coming from rescattering of pi pi via exchange of rho, sigma, f_0 mesons. Then we include the rho rho rescattering via exchange of pi, omega, a_1 mesons and finally we consider contributions of the a_1 pi rescattering via exchange of rho. The absorptive parts of amplitudes for these processes are determined. In the case of pi^+ pi^- decay mode, due to model uncertainties, the calculated contribution is |M_A| =< 1.7 x 10^-8 GeV. This produces a small relative strong phase for the tree and color-suppressed B -> pi pi amplitudes consistent with the result of a recent phenomenological analysis based on the BaBar and Belle results for the B -> pi pi branching ratios and CP asymmetries. 
Svjetlana Fajfer, Anita Prapotnik Brdnik, Tri-Nang Pham