A strong-type Furstenberg-S\'{a}rk\"{o}zy theorem for sets of positive measure

Abstract

For every $\beta\in(0,\infty)$, $\beta\neq 1$ we prove that a positive measure subset $A$ of the unit square contains a point $(x_0,y_0)$ such that $A$ nontrivially intersects curves $y-y_0 = a (x-x_0)^\beta$ for a whole interval $I\subseteq(0,\infty)$ of parameters $a\in I$. A classical Nikodym set counterexample prevents one to take $\beta=1$, which is the case of straight lines. Moreover, for a planar set $A$ of positive density we show that the interval $I$ can be arbitrarily large on the logarithmic scale. These results can be thought of as Bourgain-style large-set variants of a recent continuous-parameter S\'{a}rk\"{o}zy-type theorem by Kuca, Orponen, and Sahlsten.