arXiv subjects

Michael Jung

Publications and source records attributed to Michael Jung.

3 recordsLinked to original sources

arXiv2026

On Realisability of Twisted Homology

We discuss the question of when a homology or cohomology class with twisted integer coefficients of a manifold $X$ is realised by a submanifold. While this question is classical in nature, providing an answer requires relatively modern techniques from parametrised homotopy theory. More specifically, we introduce cobordism classes twisted by a coefficient system and then define a twisted Thom space $\operatorname{M^\mathrm{tw}O}(n)$ over $\operatorname{BO}(1)$, which serves as the classifying object for this cobordism theory under a twisted Pontryagin-Thom construction. As a result, a twisted homology class is realisable if and only if its Poincar\'e dual is the image of the twisted Thom class in $\operatorname{M^\mathrm{tw}O}(n)$ under a parametrised map $X \to \operatorname{M^\mathrm{tw}O}(n)$ over $\operatorname{BO}(1)$. Finally, we construct the parametrised Postnikov tower of $\operatorname{M^\mathrm{tw}O}(n)$ over $\operatorname{BO}(1)$ to derive obstructions to realisability and conclude by giving the first known examples of non-realisable integer homology classes in non-orientable manifolds.

math.AT↗

arXiv2023

A geometric computation of cohomotopy groups in co-degree one

Using geometric arguments, we compute the group of homotopy classes of maps from a closed $(n+1)$-dimensional manifold to the $n$-sphere for $n \geq 3$. Our work extends results from Kirby, Melvin and Teichner for closed oriented 4-manifolds and from Konstantis for closed $(n+1)$-dimensional spin manifolds, considering possibly non-orientable and non-spinnable manifolds. In the process, we introduce two types of manifolds that generalize the notion of odd and even 4-manifolds. Furthermore, for the case that $n \geq 4$, we discuss applications for rank $n$ spin vector bundles and obtain a refinement of the Euler class in the cohomotopy group that fully obstructs the existence of a non-vanishing section.

math.GT↗

arXiv2020

Characteristic Classes in Computer Algebra

We develop a framework to compute characteristic classes and their forms in the computer algebra system SageMath using symbolic calculus. In order to do this, we make use of the Chern-Weil approach in which characteristic classes of vector bundles in the de Rham cohomology are obtained by arbitrary connections. Along the way, we implement the notion of vector bundles, their sections and connections as well as mixed differential forms in SageMath. We conclude by discussing some application examples exposed in Jupyter Notebook and eventually address the issue of computational cost.

math.DG↗