Relativistic properties of spin and pion electromagnetic structure

The role of the Wigner spin rotation effects in the electromagnetic structure of pion is investigated. Pion is considered as quark--antiquark system in the framework of the instant form relativistic Hamiltonian dynamics. It is shown that the spin rotation effects give the important contribution to the pion mean square radius, to the pion form factor at the intermediate momentum transfers and to the form--factor asymptotic behaviour. The calculations are performed with the different model wave functions. It is shown that the contribution of the spin rotation depends weakly on the model for the interaction of quarks in pion. (author)