Semialgebraic methods and generalized sum-product phenomena

Yifan Jing ; Souktik Roy ; Chieu-Minh Tran

Discrete analysis (2022)

Résumé

For a bivariate $P(x,y) \in \mathbb{R}[x,y]\setminus (\mathbb{R}[x] \cup \mathbb{R}[y])$, our first result shows that for all finite $A \subseteq \mathbb{R}$, $|P(A,A)|\geq α|A|^{5/4}$ with $α=α(\mathrm{deg} P) \in \mathbb{R}^{>0}$ unless $$ P(x,y)=f(γu(x)+δu(y)) \text{ or } P(x,y)=f(u^m(x)u^n(y)) $$ for some univariate $f, u \in \mathbb{R}[t]\setminus \mathbb{R}$, constants $γ, δ\in \mathbb{R}^{\neq 0}$, and $m, n\in \mathbb{N}^{\geq 1}$. This resolves the symmetric nonexpanders classification problem proposed by de Zeeuw. Our second and third results are sum-product type theorems for two polynomials, generalizing the classical result by Erdos and Szemerédi as well as a theorem by Shen. We also obtained similar results for $\mathbb{C}$, and from this deduce results for fields of characteristic $0$ and fields of large prime characteristic. The proofs of our results use tools from semialgebraic/o-minimal geometry.

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Publié le : 2022-12-15