  We prove new and explicit formulas for the wave operators of Schroedinger
operators in R^3. These formulas put into light the very special role played by
the generator of dilations and validate the topological approach of Levinson's
theorem introduced in a previous publication. Our results hold for general (not
spherically symmetric) potentials decaying fast enough at infinity, without any
assumption on the absence of eigenvalue or resonance at 0-energy.
