Differentiable perturbation of unbounded operators
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- Kriegl, A. & Michor, P. Math. Ann. (2003) 327: 191. doi:10.1007/s00208-003-0446-5
If A(t) is a C1,α-curve of unbounded self-adjoint operators with compact resolvents and common domain of definition, then the eigenvalues can be parameterized C1 in t. If A is C∞ then the eigenvalues can be parameterized twice differentiably.