Univ Adelaide, Dept Phys & Math Phys, Adelaide, SA 5005, Australia
; Univ Adelaide, Special Res Ctr Subatom Struct Matter, Adelaide, SA 5005, Australia
; Acad Sinica, Inst High Energy Phys, Beijing 100039, Peoples R China
; Florida State Univ, Dept Phys, Tallahassee, FL 32306 USA
; Florida State Univ, Supercomp Computat Res Inst, Tallahassee, FL 32306 USA
Corrections of order 1/m(Q) (Q = b or c) to the Bethe-Salpeter (BS) equation for Lambda(Q) are analyzed on the assumption that the heavy baryon Lambda(Q) is composed of a heavy quark and a scalar, light diquark. It is found that in addition to the one BS scalar function in the limit m(Q)-->infinity, two more scalar functions are needed at the order 1/m(Q). These can be related to the BS scalar function in the leading order in our model. The six form factors for the weak transition Lambda(b)-->Lambda(c) are expressed in terms of these wave functions and the results are consistent with HQET to order 1/m(Q). Assuming the kernel for the BS equation in the limit m(Q)-->infinity to consist of a scaler confinement term and a one-gluon-exchange term we obtain numerical solutions for the BS wave functions, and hence for the hb-th, form factors to order 1/m(Q). Predictions are given for the differential and total decay widths for Lambda(b)-->Lambda(c)l<(nu)over bar>, and also for the nonleptonic decay widths for Lambda(b)-->Lambda(c) plus a pseudoscalar or vector meson, with QCD corrections being also included.