Spectral Theory of Indefinite Krein-Feller Differential Operators

The vibration of a string with a (nondecreasing) mass distribution function m leads to a generalized differential equation of second order, introduced by Krein and by Feller. The author allows also nonmonotonic functions m and hence, gets into the theory of indefinite inner product spaces. Here at the first time a systematic presentation of the generalized differential expression and of J-selfadjoint operator realizations is given. Developing a spectral theory for such Krein-Feller...
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The vibration of a string with a (nondecreasing) mass distribution function m leads to a generalized differential equation of second order, introduced by Krein and by Feller. The author allows also nonmonotonic functions m and hence, gets into the theory of indefinite inner product spaces. Here at the first time a systematic presentation of the generalized differential expression and of J-selfadjoint operator realizations is given. Developing a spectral theory for such Krein-Feller operators, the author derives the most general known criteria for the regularity of the critical point infinity. Then, by specialization, expansion theorems for wide classes of indefinite second order differential and difference operators are obtained.