Structure Theorems for the Symmetric Groups Acting on its Natural Module

Abstract: This paper gives an explicit structure theorem for the symmetric group acting on the symmetric algebra of its natural module. Let $G$ be the symmetric group on $x_1,..., x_n$ and let $d_i$ be the $i^{\text{th}}$ elementary symmetric polynomial in the $x_i$'s. We show that if we take monomial representations discussed in \cite[Section 3]{Kemper} to be the modules $V_I$, then we have an isomorphism of $kG$-modules $k[x_1,..., x_n] \cong \Oplus_{{n} \subseteq I \subseteq [n]} k[d_I] \otimes_k V_I$.