A two-parameter finite field Erdős-Falconer distance problem (1702.02126v1)

Abstract: We study the following two-parameter variant of the Erd\H os-Falconer distance problem. Given $E,F \subset {\Bbb F}q^{k+l}$, $l \geq k \ge 2$, the $k+l$-dimensional vector space over the finite field with $q$ elements, let $B{k,l}(E,F)$ be given by $${(\Vert x'-y'\Vert, \Vert x"-y" \Vert): x=(x',x") \in E, y=(y',y") \in F; x',y' \in {\Bbb F}q^k, x",y" \in {\Bbb F}_q^l }.$$ We prove that if $|E||F| \geq C q^{k+2l+1}$, then $B{k,l}(E,F)={\Bbb F}q \times {\Bbb F}_q$. Furthermore this result is sharp if $k$ is odd. For the case of $l=k=2$ and $q$ a prime with $q \equiv 3 \mod 4$ we get that for every positive $C$ there is $c$ such that $$ \text{if } |E||F|>C q^{6+\frac{2}{3}}\text{, then } |B{2,2}(E,F)|> c q^{2}.$$