Structure Dependence in $\pi \to \mathbf{\ell }\mathbf{\nu },\mathbf{\pi }\mathbf{t}\mathbf{o}\mathbf{\ell }\mathbf{\nu }\mathbf{\gamma }$ and ${\pi }^{0}to\gamma \gamma$ Decays

The amplitudes of $\pi$-meson decays are calculated in a relativistic nonperturbative quark model which assumes that mesons are made of a quark antiquark pair and of a scalar neutral component representing the contribution of the nonelementary fluctuations of the quark gluonic field. The experimental data can be fitted in a satisfactory manner using current quark masses $m_u\approx 1.5MeV,m_d\approx 9MeV$.