Orbites coadjointes et vari\'et\'es caract\'eristiques

J. Geom. Phys. 54, 1-41 (2005) The purpose of the present work is to describe a dequantization procedure for topological modules over a deformed algebra. We define the characteristic variety of a topological module as the common zeroes of the annihilator of the representation obtained by setting the deformation parameter to zero. On the other hand, the Poisson characteristic variety is defined as the common zeroes of the ideal obtained by considering the annihilator of the deformed representation, and only then setting the deformation parameter to zero. Using Gabber's theorem, we show the involutivity of the characteristic variety. The Poisson characteristic variety is indeed a Poisson subvariety of the underlying Poisson manifold. We compute explicitly the characteristic variety in several examples in the Poisson-linear case, including the dual of any exponential solvable Lie algebra. In the nilpotent case, we show that any coadjoint orbit appears as the Poisson characteristic variety of a well chosen topological module.