On the spectral properties of the Brown–Ravenhall operator

The Brown–Ravenhall operator describes an electron under a Coulomb force and subject to relativity and is defined in terms of the associated Dirac operator and the projection onto the positive spectral subspace of the free Dirac operator. For a specific optimal charge range it is known to be positive. The paper investigates the following properties of the angular momentum channels: the optimal charge range for positivity, the location and nature of the spectrum and the existence of embedded eigenvalues.