Deficiency indices and self-adjoint extensions
Research context
postgraduate concept · established · As of 2026-10-10
For a closed densely defined symmetric operator T, deficiency indices n-plus and n-minus are the dimensions of ker(T*−iI) and ker(T*+iI).
Key knowledge
For a closed densely defined symmetric operator T, deficiency indices n-plus and n-minus are the dimensions of ker(T*−iI) and ker(T*+iI). Self-adjoint extensions exist exactly when these dimensions agree, and are parameterized by unitary maps between deficiency spaces. For an initially nonclosed operator, both indices zero imply essential self-adjointness of its closure, rather than equality of the original domain with the adjoint domain.
Values and equations
n_±=dim ker(T*∓iI); extensions exist iff n_+=n_-
- T*
- Adjoint operator with its domain
- n_±
- Deficiency indices
Conditions and scope
- The closed/densely defined symmetric hypotheses and complex Hilbert space are used.
- Indices may be infinite; a formal differential expression alone does not determine them.
Sources · 1
References
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Evidence and review
Author checked this English statement, displayed equation where present and stated hypotheses against these source locations: §§1–2 unbounded domains/adjoints, §§5–6 spectral measures, §11 deficiency indices/extensions. The check is bounded to the recorded claims; no complete proof reconstruction, software proof replay or universal literature completeness is claimed.
2026-10-10 · Author source-body/statement/equation/domain check, with graph associations scoped individually. Separate independent content/source/inventory review is required before branch closure.
Entry details
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