Uncertainty in the perturbative quantum chromodynamics (PQCD) calculation of $B$ decays is investigated in $B\to \pi$, $B\to D$ transition form factors and $B\to D\pi$ decay amplitudes. $B$-meson distribution amplitude dependence is studied by taking three kinds of distribution amplitudes suggested so far. It is found that almost the same $q^2$ dependence of the form factors can be obtained irrespective of the types of the $B$-meson distribution amplitudes by suitably choosing one parameter. The $B\to D\pi$ process shows the difference due to the distribution amplitude. The effect of the subleading component of the $B$-meson distribution amplitude is also studied in the three processes. The numerical results of calculations with the subleading component can be well approximated by the leading-order calculation with a suitable choice of the distribution amplitude parameters.

• Received 11 May 2006

DOI:https://doi.org/10.1103/PhysRevD.74.014027