Decouple the Dirac Equation

In this section different methods to decouple the Dirac equation are discussed. A useful prerequisite for this reduction to two-component form is the analysis of the relationship between the large and small components of an exact eigen-solution of the Dirac equation. For every Dirac 4-spinor (f> given by equation... 

The second possibility to reduce the four-component Dirac spinor to two-component Pauli form is to decouple the Dirac equation, i.e., to transform the Dirac Hamiltonian to block-diagonal form by a suitably chosen unitary transformation U,... 

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