An improved bound for the dimension of (α, 2α)-Furstenberg sets

Abstract

We show that given α e (0, 1) there is a constant c = c α > 0 such that any planar (α, 2α)-Furstenberg set has Hausdorff dimension at least 2α + c. This improves several previous bounds, in particular extending a result of Katz–Tao and Bourgain. We follow the Katz–Tao approach with suitable changes, along the way clarifying, simplifying and/or quantifying many of the steps.