Conditional expanding bounds for two-variable functions over finite valuation rings

Abstract

In this paper, we use methods from spectral graph theory to obtain some results on the sum-product problem over finite valuation rings $\mathcal{R}$ of order $q^r$ which generalize recent results given by Hegyvári and Hennecart (2013). More precisely, we prove that, for related pairs of two-variable functions $f(x,y)$ and $g(x,y)$, if $A$ and $B$ are two sets in ${\mathcal{R}}^{\ast }$ with $|A|=|B|=q^{\alpha }$, then \[\max\left\lbrace |f(A, B)|, |g(A, B)| \right\rbrace\gtrsim |A|^{1+Δ(α)},\] for some $\Delta (\alpha )>0$.

To appear in European Journal of Combinatorics