The exclusive rare decays B -> K l(bar) l and B_c -> D(D*) l(bar) l in a   relativistic quark model
  We study the exclusive rare decay B -> K l(bar) l. We calculate the relevant form factors within a relativistic constituent quark model, for the first time without employing the impulse approximation. The calculated form factors are used to evaluate differential decay rates and polarization observables. We present results on the q2-dependence of a set of observables with and without long-distance contributions. A similar analysis is done for the exclusive rare decays B_c -> D (D*) l(bar) l with special emphasis on the cascade decay B_c -> D* (-> D pi) l(bar) l. We derive a four-fold angular decay distribution for this process in terms of helicity amplitudes including lepton mass effects. The four-fold angular decay distribution allows to define a number of physical observables which are amenable to measurement. We compare our results with the results of other studies. 
Amand Faessler (Tuebingen U.), Th. Gutsche (Tuebingen U.), M.A. Ivanov   (Dubna, JINR), J. G. Korner (Mainz U.), V.E. Lyubov...