Space-time structure of classical and quantum mechanical spin

The classical variables that define the state of a classical elementary particle are contained in the kinematical group of space-time transformations related to the Relativity Principle. Classical spin observables are expressed in terms of the velocity and orientation and their derivatives, the acceleration and angular velocity of the charge, whose motion around the center of mass produces the magnetic moment of the particle and also an oscillating electric dipole. Quantum mechanical spin operators also depend on the velocity and orientation variables and are differential operators with respect to these magnitudes. The spin structure of the photon and electron will be shown. (author)