ar X iv : m at h / 05 05 55 5 v 3 [ m at h . SP ] 2 7 M ay 2 00 5 MULTIPLE OPERATOR INTEGRALS AND HIGHER OPERATOR DERIVATIVES
نویسنده
چکیده
In this paper we consider the problem of the existence of higher derivatives of the function t → ϕ(A + tK), where ϕ is a function on the real line, A is a self-adjoint operator, and K is a bounded self-adjoint operator. We improve earlier results by Sten'kin. In order to do this, we give a new approach to multiple operator integrals. This approach improves the earlier approach given by Sten'kin. We also consider a similar problem for unitary operators.
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