  Succeeding in predicting 0^+ and 1^+ states of D and D_s heavy mesons by our
semi-relativistic quark potential model, we examine a method how to construct
Lorentz-invariant scattering amplitudes and/or decay widths and develop a
formulation to calculate Lorentz-boosted ones given the rest frame wave
functions in our model.
  To show how effective this is, we apply the formulation to calculate the
semileptonic weak form factors out of the rest frame wave functions of heavy
mesons and numerically calculate the dynamical 1/m_Q corrections to those for
the process B-bar -> D^{(*)}\ell\nu based on our model for heavy mesons. It is
shown that nonvanishing expressions for \rho_1(\omega)=\rho_2(\omega) and
\rho_3(\omega)=\rho_4(\omega)=0 are obtained in a special Lorentz frame, where
\rho_i(\omega) are the parameters used in the Neubert-Rieckert decomposition of
form factors. Various values of form factors are estimated, which are
compatible with recent experimental data as well as other theoretical
calculations.
