Normalized Derivations for Milnor's Primitive Operations on the Dickson Algebra and Applications

Abstract

We study the action of the Steenrod--Milnor operation $\mathrm{St}^{\emptyset,\Delta_i}$ on the Dickson algebra $D_n$ over $\mathbb{F}_p$. Our main observation is that normalizing by the Dickson invariant $Q_{n,0}$ yields a genuine derivation on the localization $D_n[Q_{n,0}^{-1}]$. This viewpoint provides a transparent framework to derive a closed formula for all higher iterates of $\mathrm{St}^{\emptyset,\Delta_i}$ on the Dickson generators. Consequently, we establish the vanishing condition $(\mathrm{St}^{\emptyset,\Delta_i})^m=0$ on the generators for $m\ge p$, and the stronger global operator identity $(\mathrm{St}^{\emptyset,\Delta_i})^p=0$ on all of $D_n$. Furthermore, upon localizing by $R_{n,i}^p$, the normalized action becomes Euler-type. This allows us to exactly determine the kernel and image of the derivation in the classical range $2\le i<n$, and describe them via an auxiliary grading when $i=n$. As an application, our general formalism recovers several known first-order formulas and upgrades them to closed expressions for all higher iterates. Finally, we present an ordinary Koszul-type construction attached to normalized-ratio coefficients, providing a structural analogy to Margolis homology for operations on the $\xi$-side that do not necessarily square to zero.