I am interested in understanding how is done the resolvent set (actually, I am only interested in proving that it is non-empty) of the free Dirac operator $$ H_0 = -i\alpha\cdot\nabla + m\beta$$ where $D(H_0) = H^{1}(\mathbb{R}^3;\mathbb{C}^4)$. I am also interested in what happens to the resolvent set of the pertubated operator $H_0+ kV$ where $V$ is a potential.
Could anyone hlep or give me some references?
Thank you in advance!