Semileptonic form factors: A model-independent approach

We demonstrate that the $\overrightarrow{B}{D}^{\left(*\right)}l\nu$ form factors can be accurately predicted given the slope parameter ${\rho }^2$ of the Isgur-Wise function. Only weak assumptions, consistent with lattice results, on the wave function for the light degrees of freedom are required to establish this result. We observe that the QCD and ${1/m}_Q$ corrections can be systematically represented by an effective Isgur-Wise function of shifted slope. This greatly simplifies the analysis of semileptonic B decay. We also investigate what the available semileptonic data can tell us about lattice QCD and heavy quark effective theory. A rigorous identity relating the form factor slope difference ${\rho }_{D^{*}}^2-{\rho }_{A_1}^2$ to a combination of form factor intercepts is found. The identity provides a means of checking theoretically evaluated intercepts with experiment.