Covariant Abstract Description for a Dirac Particle

摘要

We give a direct link between covariant description of Dirac particles in the abstract framework of unitary representation of the Poincare group and description with the help of the Dirac equation. In this context we discuss the spin operator for a relativistic Dirac particle. We show also that the spin operator used in quantum field theory for spin s = 1/2 corresponds to the Foldy-Wouthuysen mean-spin operator. We hope that this formalism will be useful in the theory of relativistic quantum information.