  A field theoretic description for inclusive semileptonic B meson decays is
formulated. We argue that large regions of the phase spaces for the decays are
dominated by distances near the light cone. The light-cone dominance allows to
incorporate nonperturbative QCD effects in a distribution function. A
one-to-one correspondence with the heavy quark effective theory is developed,
which can estimate the first two moments of the distribution function. These
conditions are useful but not restrictive enough to specify the distribution
function, which must still be determined from experiment. Several
model-independent predictions, such as scaling, sum rules of the hadronic
structure functions and relations among them, are made. General formulas for
the differential decay rates on several variables are presented, which are used
for calculating the electron energy spectra with an Ansatz for the light-cone
distribution function.
