The semileptonic and leptonic decays of heavy mesons are studied as a
phenomenological application and exploration of a heavy-quark limit of
Dyson-Schwinger equations. The single form factor, ξ(w), which
characterises the semileptonic decay in this limit, is calculated and compares
well with recent experimental extractions. We obtain a lower bound of 1/3 on
the slope-parameter ρ2≡−ξ′(1), which, in calculations with
realistic input, is exceeded by a great deal: agreement with experimental data
requiring ρ2∼1.2−1.6. The flavour and momentum dependence of the
light-quark propagators has observable consequences.Comment: 11 pages, LaTeX, epsfig.sty, elsart.st
