  The thesis is devoted to the phase space representation of relativistic
quantum mechanics. For a class of observables with matrix-valued Weyl symbols
proportional to the identity matrix, the Weyl-Wigner-Moyal formalism is
proposed. The evolution equations are found to coincide with their counterparts
in relativistic quantum mechanics with non-local Hamiltonian. The difference
between the theories is connected with peculiarities of the constraints on the
initial conditions. Effective increase in coherence between eigenstates of the
Hamiltonian is found. Relativistic coherent states that take into account a
non-trivial charge structure of the position and momentum operators and satisfy
the charge superselection rule are considered. On this basis, the entangled
coherent states are developed.
