Schweizer, BenUrban, Maik2019-08-022019-08-022019-04http://hdl.handle.net/2003/3815710.17877/DE290R-20136We prove a limiting absorption principle for sesquilinear forms on Hilbert spaces and apply the abstract result to a Helmholtz equation with radiation condition. The limiting absorption principle is based on a Fredholm alternative. It is applied to Helmholtz-type equations in a truncated waveguide geometry. We analyse a problem with radiation conditions on truncated domains, recently introduced in [4]. We improve the previous results by treating the limit δ→0 .enPreprint;2019-02610preprint