A Non-Linear Roth Theorem for Sets of Positive Density

Ben Krause

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arXiv · 1901.01371

A Non-Linear Roth Theorem for Sets of Positive Density

Ben Krause

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Abstract

Suppose that $A \subset \mathbb{R}$ has positive upper density, \[ \limsup_{|I| \to \infty} \frac{|A \cap I|}{|I|} = \delta > 0,\] and $P(t) \in \mathbb{R}[t]$ is a polynomial with no constant or linear term, or more generally a non-flat curve: a locally differentiable curve which doesn't "resemble a line" near $0$ or $\infty$. Then for any $R_0 \leq R$ sufficiently large, there exists some $x_R \in A$ so that \[ \inf_{R_0 \leq T \leq R} \frac{|\{ 0 \leq t < T : x_R - t \in A, \ x_R - P(t) \in A \}|}{T} \geq c_P \cdot \delta^2 \] for some absolute constant $c_P > 0$, that depends only on $P$.

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Ben Krause. 2019-01-05. A Non-Linear Roth Theorem for Sets of Positive Density. https://arxiv.org/abs/1901.01371

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