2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/42311We calculate the branching ratios of $B_{s,d}\to γγ$ decay in the sequential fourth generation model. We find that the theoretical values of the branching ratios, ${\rm BR}(B_{s}\toγγ)$, including the contributions of $t'$, are much different from the minimal standard model (SM) predictions. The new physics contribution can provide one to two orders enhancement to the standard model prediction of ${\rm BR}(B_{s}\toγγ)$. But due to the tiny values of 4th generation CKM matrix element $V_{t'd}^* V_{t'b}$, the new physics effect on ${\rm BR}(B_{d}\toγγ)$ is very small and can not be distinct from the SM prediction. It is shown that the decay $B_s\to γγ$ can give the test of new physics signals from the 4th generation model.20 pages, 6 figuresHigh Energy Physics - Phenomenologytext