RARE DECAYS B-](K,K-ASTERISK)(L(-),NU(NU)OVER-BAR) IN THE QUARK-MODEL()L()

Long-distance effects in exclusive rare semileptonic transitions B --> (K,K) are analysed within a relativistic quark model. The meson tran sition form factors, describing the meson amplitudes of the effective weak Hamiltonian, are calculated within the dispersion formulation of the quark model as relativistic double spectral representations throug h the wave functions of the initial and final mesons. The dilepton spe ctra and lepton asymmetries are considered within the framework provid ed by the Standard Model. It is found that, while the non-resonant dec ay rates are very sensitive to quark model parameters, the model depen dence of the predicted dilepton forward-backward and lepton polarizati on asymmetries is remarkably small, providing only an overall similar to 10% uncertainty. (C) 1997 Elsevier Science B.V.