New effective treatment of the light-front nonvalence contribution in timelike exclusive processes

We discuss a necessary nonvalence contribution in timelike exclusive processes. Following a Schwinger-Dyson type of approach, we relate the nonvalence contribution to an ordinary light-front wave function that has been extensively tested in the spacelike exclusive processes. A complicate four-body energy denominator is exactly cancelled in summing the light-front time-ordered amplitudes. Applying our method to K ℓ3 and D 0 → K − ℓ + ν l where a rather substantial nonvalence contribution is expected, we find not only an improvement in comparing with the experimental data but also a covariance(i.e. frame-independence) of existing light-front constituent quark model. With the wealth of new and upgraded B-meson factories, exclusive decay processes will be studied intensively. Unlike the leading twist structure functions measured in deep inelastic scattering, such exclusive channels are sensitive to the structure of the hadrons at the amplitude level and to the coherence between the contributions of the various quark currents and multi-parton amplitudes. The central unknown required for reliable calculations of weak decay amplitudes are thus the hadronic matrix elements. Perhaps, one of the most popular formulations for the analysis of exclusive processes involving hadrons may be provided in the framework of light-front (LF) quantization [1]. In particular, the Drell-Yan-West (q + = q 0 + q 3 = 0) frame has been extensively used in the calculation of various electroweak form factors and decay processes [2–4]. As an example, only the parton-number-conserving (valence) Fock state contribution is needed in q + = 0 frame when the " good " component of the current, J + or J ⊥ = (J x , J y), is used for the spacelike electromagnetic form factor calculation of pseudoscalar mesons. The LF approach may also provide a bridge between the two fundamentally different pictures of *