Eigenvalue accumulation and bounds for non-selfadjoint matrix differential operators related to NLS
Christiane TretterUniversität Bern, Switzerland
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We establish results on the accumulation and location of the non-real spectrum of non-selfadjoint matrix differential operators arising in the study of non-linear Schrödinger equations (NLS) in . In particular, without restrictions on the decay rate of the potentials to at , we show that the non-real spectrum cannot accumulate anywhere on the real axis. Under some weak assumptions satisfied, e.g., by -potentials with , , we prove that there are only finitely many non-real eigenvalues and that the non-real eigenvalues are located in a bounded lens-shaped region centered at the origin. Our key tool to prove this is a recent result on the existence of -semi-definite invariant subspaces for -selfadjoint operators in Krein spaces as well as abstract operator matrix methods.