The symbol of a function of an operator
arXiv:math/0411163
Abstract
We give an explicit formula for the symbol of a function of an operator. Given an operator {\hat A} on L^2(R^N) with symbol A, and a function f, we obtain the symbol of f(\hat A) in terms of A. As an application, Bohr-Sommerfeld quantization rules are explicitely calculated at order 4 in hbar.
26 pages. v2 contains a better, shorter proof. The problem is considered in more generality. References are corrected