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Alex D. Austin

Publications and source records attributed to Alex D. Austin.

3 recordsLinked to original sources
arXiv2020

The contact mappings of a flat $(2,3,5)$-distribution

Let $Ω$ and $Ω'$ be open subsets of a flat $(2,3,5)$-distribution. We show that a $C^1$-smooth contact mapping $f : Ω\to Ω'$ is a $C^\infty$-smooth contact mapping. Ultimately, this is a consequence of the rigidity of the associated stratified Lie group (the Tanaka prolongation of the Lie algebra is of finite-type). The conclusion is reached through a careful study of some differential identities satisfied by components of the Pansu-derivative of a $C^1$-smooth contact mapping.

math.DG↗
arXiv2020

Logarithmic Potentials and Quasiconformal Flows on the Heisenberg Group

Let $\mathbb{H}$ be the sub-Riemannian Heisenberg group. That $\mathbb{H}$ supports a rich family of quasiconformal mappings was demonstrated by Korányi and Reimann using the so-called flow method. Here we supply further evidence of the flexible nature of this family, constructing quasiconformal mappings with extreme behavior on small sets. More precisely, we establish criteria to determine when a given logarithmic potential $Λ$ on $\mathbb{H}$ is such that there exists a quasiconformal mapping of $\mathbb{H}$ with Jacobian comparable to $e^{2Λ}$ (so that the Jaobian is zero or infinity at the same points as $e^{2Λ}$). When $Λ$ is continuous and meets the criteria, we show the canonical (sub-Riemannian) metric $g_0$ and the weighted metric $g = e^Λg_0$ generate bi-Lipschitz equivalent distance functions. These results rest on an extension to the theory of quasiconformal flows on $\mathbb{H}$ and constructions that adapt the iterative method of Bonk, Heinonen, and Saksman.

math.CA↗