Analytic continuations with respect to a parameter of the Green function of exterior boundary value problems for the two-dimensional Helmholtz equation. II
Abstract:
This paper gives a construction of some special potentials for the two-dimensional Helmholtz equation. With these potentials, one can establish the existence of Green's functions of exterior boundary-value problems for each $k$ from the complex upper $k$-plane, and the analyticity of these functions in that region. More than that, one can establish the existence of an analytic continuation to the region
$$
\{0>\operatorname{Im}k>-\beta(1+|\operatorname{Re}k|^{1/3},\,|\operatorname{Re}k|>0\}
$$
for some $\beta>0$, with estimates characterizing the behavior of the Green functions for large absolute values of $k$.
Bibliography: 6 titles.