B -> pi pi decays
  The branching ratios and CP asymmetries of   $B\to \pi\pi$ decays measured in B factory experiments indicate a large ratio of color-suppressed ($C$) to color-allowed ($T$) tree contributions and a large relative phase between the tree and penguin amplitude. In this talk, I would like to report on a recent analysis to see whether the large $C/T$ ratio can be explained within the QCD based model with i) a large contribution from the annihilation terms or with ii) large final-state-interaction phase between two different isospin amplitudes. We show that the current experimental data do not exclude either possibility but we may be able to distinguish these two effects in future measurements of direct CP asymmetry in $B\to \pi^{0}\pi^{0}$ decay. 
T. N. Pham