Soft-momentum quark-model predictions for the pseudoscalar-meson decays into lepton pairs

The pseudoscalar decays P→l+l- are driven by second-order electromagnetic loop diagrams which are rendered finite by use of appropriate off-shell P→γγ form factors determined in the quark model. The theoretical predictions using the soft-momentum limit are in reasonable agreement with the experimental rates and branching ratios, the latter being approximately twice the unitarity bounds for the decays π0→e+e-, eta→μ+μ-, and K/sub L/0→μ+μ-. We also investigate the radiative decays π0→e+e-γ and eta→μ+μ-γ in the same model, and deduce that one cannot extract unambiguously the constituent quark masses from the experimental data