Form factors and branching ratios of the FCNC $B\to a_1{\mathrm{\ell }}^{+}{\mathrm{\ell }}^{-}$ decays

We analyze the semileptonic $B\to a_1{\mathrm{\ell }}^{+}{\mathrm{\ell }}^{-}$, $\mathrm{\ell }=\tau ,\mu ,e$ transitions in the frame work of the three-point QCD sum rules in the standard model. These rare decays governed by flavor-changing neutral current transition of $b\to d$. Considering the quark condensate contributions, the relevant form factors as well as the branching fractions of these transitions are calculated.