Spectral theory for symmetric systems in an exterior domain (Q1109230)

The author studies spectral problems for the operator \[ H(x,D)u=\sum^{n}_{j=1}A_ j(x)\partial u/\partial x_ j+C(x)u\quad (x\in \Omega) \] in an exterior domain \(\Omega\) of \({\mathbb{R}}^ n\); here \(u=(u_ 1,...,u_ d)\) is a \({\mathbb{C}}^ d\)-valued function, and \(A_ j\) and C are \(d\times d\)-matrix valued coefficients. The basic tool is the commutator method developed by \textit{E. Mourre} [Commun. Math. Phys. 78, 391-408 (1981; Zbl 0489.47010)].