Orbites Nilpotentes Sphériques et Représentations unipotentes associées: Le cas $\bf SL_n$

Let $G$ be a real simple Lie group and $\mathfrak g$its Lie algebra. Given a nilpotent adjoint $G$-orbit $O$, the question is to determine the irreducible unitary representations of $G$ that we can associate to $O$, according to the orbit method. P. Torasso gave a method to solve this problem if $O$ is minimal. In this paper, we study the case where $O$ is any spherical nilpotent orbit of $sl_n({\mathbb R})$, we construct, from $O$, a family of representations of the two-sheeted covering of $SL_n({\mathbb R})$with Torasso's method and, finally, we show that all these representations are associated to the corresponding orbit.