Computation of unitary group for the Rashba spin-orbit coupled operator, with application to point-interactions

We compute an explicit formula for the one-parameter unitary group of the single-particle Rashba spin-orbit coupled operator in dimension three. As an application, we derive the formula for the Green function for the two-particle operator, and then prove that the spin-dependent point-interaction is of class ${\mathcal{H}}_{-4}$. The latter is thus the example of a supersingular perturbation for which no self-adjoint operator can be constructed.