The Foldy—Wouthuysen Representation for Free Particles
As discussed in the previous chapters, the spinors in the Dirac theory consist of four components. In the nonrelativistic limit, for spinors belonging to positive (negative) energy states, the upper (lower) two components beecome large compared to the lower (uppeer) two components [cf. (2.44), (2.72)]. The question arises, whether there exists a representation that reflects this property as a general feature, i.e. also for large velocities of the particles.
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- 1.This is discussed in more detail in W. Greiner, J. Reinhardt: Quantum Electrodynamics, 2nd ed. ( Springer, Berlin, Heidelberg 1994 ).Google Scholar