A theory on perturbations of the Dirac operator
The author considers perturbations of the first order differential operator with \(2\times 2\) matrix coefficients (the Dirac operator) which has one singular point that is allowed to be either zero or infinity. Using unitary transformations he gives for limit point type operators and limit circle type operators necessary and sufficient conditions for the perturbations to be relatively bounded or relatively compact with respect to the Dirac operator.
scientific article; zbMATH DE number 1374887