Exact Light-Cone Wavefunction Representation of Matrix Elements of Electroweak Current

The matrix elements of electroweak currents which occur in exclusive decays of heavy hadrons are evaluated in the nonperturbative light-cone Fock representration. In general, each semileptonic exclusive decay amplitude receives two contributions, a diagonal $\Delta n = 0$ parton-number-conserving amplitude and a $\Delta n = -2$ contribution in which a quark and an antiquark from the initial hadron Fock state annihilate to the leptonic current. The general formalism can be used as a basis for systematic approximations to heavy hadron decay amplitudes such as hard perturbative QCD contributions. We illustrate the general formalism using a simple perturbative model of composite hadrons. Our analysis demonstrates the occurence of "zero-mode" endpoint contributions to matrix elements of the "bad" $j^-$ currents in the Drell-Yan frame when $q^+ \to 0$.