Generalized polynomials and hyperplane functions in $(\mathbb{Z}/p^k\mathbb{Z})^n$

Abstract: For $p$ prime, let $\mathcal{H}<sup>n$ be the linear span of characteristic functions of hyperplanes in $(\mathbb{Z}/p<sup>k\mathbb{Z})<sup>n$. We establish new upper bounds on the dimension of $\mathcal{H}<sup>n$ over $\mathbb{Z}/p\mathbb{Z}$, or equivalently, on the rank of point-hyperplane incidence matrices in $(\mathbb{Z}/p<sup>k\mathbb{Z})<sup>n$ over $\mathbb{Z}/p\mathbb{Z}$. Our proof is based on a variant of the polynomial method using binomial coefficients in $\mathbb{Z}/p<sup>k\mathbb{Z}$ as generalized polynomials. We also establish additional necessary conditions for a function on $(\mathbb{Z}/p<sup>k\mathbb{Z})<sup>n$ to be an element of $\mathcal{H}<sup>n$.