Eigenvalues Dirac free-particle

The four normalized free-particle Dirac eigenspinors of section 5.3 with shifted eigenvalues e —nteC may now be written as... 

We now return to the problem of the negative-energy solutions that appeared when we solved the free particle Dirac equation in the previous chapter. The energy eigenvalues obtained there were either + = or = - /nfic + p c. The... 

Note that the derivation of the Dirac equation in chapter 5 holds for any freely moving spin-1 /2 fermion and hence also for the proton we come back to such general two-particle Hamiltonians at the beginning of chapter 8 (for an explicit solution of the corresponding two-fermion eigenvalue equation we refer the reader to the work by Marsch [112-115]). In the field-free Dirac Hamiltonian only the rest mass determines which fermion is considered. Accordingly, the total wave function of the hydrogen atom reads... 

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