Heavy Meson Observables and Dyson-Schwinger Equations
  Dyson-Schwinger equation (DSE) studies show that the b-quark mass-function is approximately constant, and that this is true to a lesser extent for the c-quark. These observations provide the basis for a study of the leptonic and semileptonic decays of heavy pseudoscalar mesons using a ``heavy-quark'' limit of the DSEs. When exact, this limit reduces the number of independent form factors. Semileptonic decays with light mesons in the final state are also accessible because the DSEs provide a description of light-quark propagation characteristics and light-meson structure. A description of B-meson decays is straightforward, however, the study of decays involving the D-meson indicates that c-quark mass-corrections are quantitatively important. 
M. A. Ivanov, Yu. L. Kalinovsky, P. Maris and C. D. Roberts