Invariant differential operators and the generalized symmetric group

In this paper we study the decomposition of the direct image of $\pi_+(\Oc_{X})$ the polynomial ring $\Oc_X$ as a $\D$-module, under the map $\pi: \spec \Oc_{X} \to \spec \Oc_{X}^{G(r,n)}$, where $\Oc_{X}^{G(r,n)}$ is the ring of invariant polynomial under the action of the wreath product $G(r,p):= \ZZ / r \ZZ \wr \Sc_n$. We first describe the generators of the simple components of $\pi_+(\Oc_X)$ and give their multiplicities. Using an equivalence of categories and the higher Specht polynomials, we describe a $\D$-module decomposition of the polynomial ring localized at the discriminant of $\pi$. Furthermore, we study the action invariants, differential operators, on the higher Specht polynomials.