Abstract
We prove that, under certain conditions on the function pair ϕ1 and ϕ2, the bilinear average \({q^{- 1}}\sum\nolimits_{y \in {\mathbb{F}_q}} {{f_1}\left({x + {\varphi _2}\left(y \right)} \right){f_2}\left({x + {\varphi _2}\left(y \right)} \right)} \) along the curve (ϕ1, ϕ2) satisfies a certain decay estimate. As a consequence, Roth type theorems hold in the setting of finite fields. In particular, if \({\varphi _1},{\varphi _2} \in {\mathbb{F}_q}\left[X \right]\) with ϕ1(0) = ϕ2(0) = 0 are linearly independent polynomials, then for any \(A \subset {\mathbb{F}_q},\left| A \right| = \delta q\) with δ > cq−1/12, there are ≳ δ3q2 triplets x, x+ϕ1(y), x + ϕ2(y) ∈ A. This extends a recent result of Bourgain and Chang who initiated this type of problems, and strengthens the bound in a result of Peluse, who generalized Bourgain and Chang’s work. The proof uses discrete Fourier analysis and algebraic geometry.
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Dong, D., Li, X. & Sawin, W. Improved estimates for polynomial Roth type theorems in finite fields. JAMA 141, 689–705 (2020). https://doi.org/10.1007/s11854-020-0113-8
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DOI: https://doi.org/10.1007/s11854-020-0113-8