New physical effects on the decay $B_{s(d)} \to \gamma\gamma$ in the   sequential fourth Generation model
  We study the contributions to the branching ratios of $B_{s(d)}\to \gamma \gamma$ decay in the sequential fourth generation model (SM4). We find that the theoretical values of the branching ratios, ${\rm BR}(B_{s(d)}\to\gamma\gamma)$, including the contributions of $m_{t'}$ and the new $4 \times 4$ CKM (CKM4) matrix factors, $|V^{*}_{t's}V_{t'b}|$ and $|V^{*}_{t'd}V_{t'b}|$, are much different from the minimal standard model (SM) predictions. The new physics effects, especially contributed from the CKM4 matrix factors, can provide more than one order enhancement to the SM prediction. It is shown that the decay $B_{s(d)}\to \gamma \gamma$ can test the new physics signals from SM4. 
H. Chen and W. Huo
hep-ph