Relativistic Covariant Equal-Time Equation For Quark-Diquark System

Relativistic three-dimensional quasipotential (equal-time) equations are considered, which describe bound states of fermion and boson of spin S=0 or S=1. The spin structure of the interaction quasipotentials in such systems is studied, and corresponding partial-wave equation for the simplest case is obtained. Such equations can be used in calculations of energy spectra, decay rates and structure functions of quark-diquark systems (nucleons and their resonances) as well as for description of ($\pi \mu$)- atom.