Study of Rare $B_c^{+}\to D_{d,s}^{(\ast )+}l\bar{l}$ Decays

We study the rare decays of $B_c^{+}\to D_q^{(\ast )+}l\bar{l}$ ($q=d,s$ and $l={\nu }_l,e,\mu ,\tau )$ in the standard model. The form factors are evaluated in the light front and constituent quark models, respectively. We find that the decay branching ratios calculated in the two models for $B_c^+\to D^+_q l\bar{l}$agreewellwitheachother,whereasthosefor$B_c^+\to D_q^{*+}l\bar{l}$ are different.