A priori estimates for the Helmholtz equation with electromagnetic potentials in exterior domains

We study the Helmholtz equation with electromagnetic-type perturbations, in the exterior of a domain, in dimension $n\ge 3$. We prove, by multiplier techniques in the sense of Morawetz, a family of a priori estimates from which the limiting absorption principle follows. Moreover, we give some standard applications to the absence of embedded eigenvalues and zero-resonances, under explicit conditions on the potentials.