Shirokov canonical parameterization of local operators in modern problems of the hadron structure

We discuss the general method of parameterization of matrix elements of local operators developed by Yu. M. Shirokov. This method is a core of one of the successful variants of the relativistic composite model developed by the authors, namely, the instant form of Dirac relativistic dynamics, which gives good results when describing composite quark and nucleon systems. Using the Shirokov parameterization, we construct operators of the electromagnetic current and the energy–momentum tensor of a composite system taking the Lorentz covariance and the conservation into account. As an example, we derive formulas for the electric and gravitational form factors of a pion.