Lino Joss Fidel Haupt

Office 3342

Ernst Abbe Platz 2

07743 Jena, Germany

I am a doctoral candidate supervised by Prof. Dr. Tobias Jäger working in the Research group Dynamical Systems at the Institute of Mathematics of the Friedrich-Schiller-University Jena.

During the current winter semester, I give the lecture on point-set topology. My principal research interests are finite-to-one extensions, in the almost, almost-surely and measure theoretical sense, of equicontinuous systems and corresponding notions of multivariate frequent stability, diam-mean equicontinuity and mean equicontinuity.

recent publications

Multivariate mean equicontinuity for finite-to-one topomorphic extensions

Jonas Breitenbücher, Lino Haupt, and Tobias Jäger

2024

Abs arXiv

In this note, we generalise the concept of topo-isomorphic extensions and define finite topomorphic extensions as topological dynamical systems whose factor map to the maximal equicontinuous factor is measure-theoretically at most m-to-one for some m ∈ ℕ. We further define multivariate versions of mean equicontinuity, complementing the notion of multivariate mean sensitivity introduced by Li, Ye and Yu, and then show that any m-to-one topomorphic extension is mean (m+1)-equicontinuous. This falls in line with the well-known result, due to Downarowicz and Glasner, that strictly ergodic systems are isomorphic extensions if and only if they are mean equicontinuous. While in the multivariate case we can only conjecture that the converse direction also holds, the result provides an indication that multivariate equicontinuity properties are strongly related to finite extension structures. For minimal systems, an Auslander-Yorke type dichotomy between multivariate mean equicontinuity and sensitivity is shown as well.
Construction of smooth isomorphic and finite-to-one extensions of irrational rotations which are not almost automorphic

Lino Haupt, and Tobias Jäger

2023

Abs arXiv

Due to a result by Glasner and Downarowicz, it is known that a minimal system is mean equicontinuous if and only if it is an isomorphic extension of its maximal equicontinuous factor. The majority of known examples of this type are almost automorphic, that is, the factor map to the maximal equicontinuous factor is almost one-to-one. The only cases of isomorphic extensions which are not almost automorphic are again due to Glasner and Downarowicz, who in the same article provide a construction of such systems in a rather general topological setting. Here, we use the Anosov-Katok method in order to provide an alternative route to such examples and to show that these may be realised as smooth skew product diffeomorphisms of the two-torus with an irrational rotation on the base. Moreover - and more importantly - a modification of the construction allows to ensure that lifts of these diffeomorphism to finite covering spaces provide novel examples of finite-to-one topomorphic extensions of irrational rotations. These are still strictly ergodic and share the same dynamical eigenvalues as the original system, but show an additional singular continuous component of the dynamical spectrum.