HEAVY-TO-HEAVY AND HEAVY-TO-LIGHT FORM-FACTORS FOR WEAK DECAYS IN THELIGHT-FRONT APPROACH - EXCLUSIVE O--TO-O- CASE

Form factors for weak transitions between heavy pseudoscalar mesons ar e investigated within a relativistic quark model formulated on the Lig ht front. It is shown that the light-front result derived in the timel ike region for the matrix elements of the plus-component of the weak v ector current coincides with the spectator pole term of the quark tria ngle diagram, For the first time, the dependence of the form factors o n the squared 4-momentum transfer q(2) is calculated in the whoe kinem atical region 0 less than or equal to q(2) less than or equal to q(max )(2). The equal-time wave functions corresponding to the updated versi on of the Isgur-Scora-Grinstein-Wise model are adopted for numerical i nvestigations of the semileptonic decays B --> Dlv(l), B --> pi lv(l), and D --> Klv(l). The results for the form and the decay rates are pr esented and compared with available experimental data and predictions of various approaches. The decay K-L(0) --> pi(+/-)e(-/+)v(e) is brief ly discussed. The results of our approach are consistent with experime ntal data.