A study on the rare radiative decay $B_c \to D_s^*\gamma$ in technicolor   with scalars
  Applying the perturbative QCD (PQCD), we study the process $B_c\rightarrow D_s^*\gamma$ in the technicolor with a massless scalar doublet model (TCMLSM) recently presented by C. D. Carone and H. Georgi; and compare the results with that estimated in the standard model (SM). There are two mechanisms which contribute to the $B_c\rightarrow D_s^* \gamma$ process. One proceeds through the short distance $b\rightarrow s \gamma$ transition, the other through weak annihilation accompanied by a photon emission. In the SM, these two processes are found to contribute with the same order of magnitude. In the TCMLSM, the modification of $B_c\rightarrow D_s^*\gamma$ from $\pi_p$ (the physical pions in this model) is small for the allowed mass of $\pi_p$. 
Gongru Lu, Yigang Cao, Zhaohua Xiong and Zhenjun Xiao