The $k$-resultant modulus set problem on algebraic varieties over finite fields

Abstract

We study the $k$-resultant modulus set problem in the $d$-dimensional vector space $\mathbb F_q^d$ over the finite field $\mathbb F_q$ with $q$ elements. Given $E\subset \mathbb F_q^d$ and an integer $k\ge 2$, the $k$-resultant modulus set, denoted by $\Delta_k(E)$, is defined as $$ \Delta_k(E)=\{\|x^1\pm x^2 \pm \cdots \pm x^k\|\in \mathbb F_q: x^j\in E, ~j=1,2,\ldots, k\},$$ where $\|\alpha\|=\alpha_1^2+\cdots+ \alpha_d^2$ for $\alpha=(\alpha_1, \ldots, \alpha_d) \in \mathbb F_q^d.$ In this setting, the $k$-resultant modulus set problem is to determine the minimal cardinality of $E\subset \mathbb F_q^d$ such that $\Delta_k(E) = \mathbb F_q$ or $\mathbb{F}_q^*$. This problem is an extension of the Erd\H{o}s-Falconer distance problem. In particular, we investigate the $k$-resultant modulus set problem with the restriction that the set $E\subset \mathbb F_q^d$ is contained in a specific algebraic variety. Energy estimates play a crucial role in our proof.