$B^0 \to \phi\phi$ Decay in Perturbative QCD Approach
  The rare decay $B^0 \to \phi\phi$ can occur only via penguin annihilation topology in the standard model. We calculate this channel in the perturbative QCD approach. The predicted branching ratio is very small at ($10^{-8}$). We also give the polarization fractions, which shows that the transverse polarization contribution is comparable to the longitudinal one, due to a big transverse contribution from factorizable diagrams.   The small branching ratio in SM, makes it sensitive to any new physics contributions. 
Cai-Dian L\"u, Yue-long Shen, Jin Zhu