Tangents and pointwise Assouad dimension of invariant sets

Antti Käenmäki, Alex Rutar

Published 2023-09-21Version 1

We study the fine scaling properties of sets satisfying various weak forms of invariance. Our focus is on the interrelated concepts of (weak) tangents, Assouad dimension, and a new localized variant which we call the pointwise Assouad dimension. For general attractors of possibly overlapping bi-Lipschitz iterated function systems, we establish that the Assouad dimension is given by the Hausdorff dimension of a tangent at some point in the attractor. Under the additional assumption of self-conformality, we moreover prove that this property holds for a subset of full Hausdorff dimension. We then turn our attention to an intermediate class of sets: namely planar self-affine carpets. For Gatzouras--Lalley carpets, we obtain precise information about tangents which, in particular, shows that points with large tangents are very abundant. However, already for Bara\'nski carpets, we see that more complex behaviour is possible.