We consider the scalar form factor in the weak current matrix element <PK|jμ|0>, P=π, η, η′. It obtains the contributions from the scalar meson resonance [Formula: see text] and from the scalar projection of the vector meson K*(892) resonance. We analyze decay amplitudes of the Cabibbo suppressed decays D → KP, P=π, η, η′ using the factorization approach. The form factors of the relevant matrix elements are described by assuming the dominance of nearby resonances. The annihilation contribution in these decays arises from the matrix element <PK|jμ|0>. All the required parameters are experimentally known except the scalar meson [Formula: see text] decay constant. We fit the decay amplitudes and we find that final state interaction improves the agreement with the experimental data. Then we extract bounds on scalar form factor parameters and compare them with the experimental data obtained in the analyses of K→πeνe and K→πμνμ. The same scalar form factor is present in the τ → KPντ decay, with P=π, η, η′. Using the obtained bounds we investigate the significance of the scalar meson form factor in the τ→ KPντ, P=π, η, η′ decay rates and spectra. We find that the [Formula: see text] scalar meson dominates in the τ→Kη′ντ decay spectrum.
Scalar form factor of the nucleon and nucleon-scalar meson coupling constant in QCD
