Florian Kranhold

[Florian Kranhold]

Address Mathematical Institute
University of Bonn
Endenicher Allee 60
53115 Bonn
Room4.020
Phone+49 (0)228 73-62208
Mail
PGP Public Key (0xD2890F65)

I am a postdoctoral researcher in the working group of Carl-Friedrich Bödigheimer. My research interests lie in the area of algebraic topology: more specifically, I am interested in (coloured) topological operads and their algebras, configuration spaces and their homological stability, as well as diffeomorphism groups and mapping class groups, moduli spaces of surfaces and their (unstable) homology. More recently, I have been studying low-dimensional equivariant and parametrised cobordism cate­go­ries and their homotopy type.

Here is my CV and my ORCID record, and you can watch a Zoom talk I gave in the Purdue Topology Seminar in September 2021, as well as a Talk at a blackboard I gave at a Workshop in Co­pen­hagen in November 2021.


Research

  • Computations in the unstable homology of moduli spaces of Riemann surfaces

    In this article we give a survey of homology computations for moduli spaces \(\smash{\mathfrak{M}_{\smash{g,1}}^m}\) of Riemann surfaces with genus \(g\geqslant 0\), one boundary curve, and \(m\geqslant 0\) punctures. While rationally and stably this question has a satisfying answer by the Madsen–Weiss theorem, the unstable homology remains notoriously complicated. We discuss calculations with integral, mod-2, and rational coefficients. Furthermore, we determine, in most cases, explicit generators using homology operations

  • Parametrised moduli spaces of surfaces as infinite loop spaces

    We study the \(E_2\)-algebra \(\Lambda\mathfrak{M}_{*,1}=\coprod_{g\geqslant 0}\Lambda\mathfrak{M}_{g,1}\) consisting of free loop spaces of moduli spaces of Riemann surfaces with one parametrised boundary component, and compute the homotopy type of the group completion \(\Omega B\Lambda\mathfrak{M}_{*,1}\): it is the product of \(\Omega^\infty\mathbf{MTSO}(2)\) with a certain free \(\Omega^\infty\)-space depending on the family of all boundary-irreducible mapping classes in all mapping class groups \(\Gamma_{g,n}\) with \(g\geqslant 0\) and \(n\geqslant 1\).

  • Configuration spaces of clusters as \(E_d\)-algebras

    It is a classical result that configuration spaces of labelled particles in \(\mathbb{R}^d\) are free algebras over the little \(d\)-cubes operad \(\mathscr{C}_d\), and their \(d\)-fold bar construction is equivalent to the \(d\)-fold suspension of the labelling space. The aim of this paper is to study a variation of these spaces, namely the configuration space of labelled clusters of points in \(\mathbb{R}^d\). This configuration space is again an \(E_d\)-algebra, but in general not a free one. We give geometric models for their iterated bar construction in two different ways: one uses an additional verticality constraint, and the other one uses a description of these clustered configuration spaces as cellular \(E_1\)-algebras. In the last section, we show a stable splitting result and present some applications.

  • Vertical configuration spaces and their homology

    We introduce ordered and unordered configuration spaces of ‘clusters’ of points in an Euclidean space \(\mathbb{R}^d\), where points in each cluster have to satisfy a ‘verticality’ condition, depending on a decomposition \(d=p+q.\) We compute the homology in the ordered case and prove homological stability in the unordered case.

Theses

  • Coloured topological operads and moduli spaces of surfaces with multiple boundary curves

    This is my PhD thesis which was finished in January 2022 under the supervision of Carl-Friedrich Bödigheimer.

  • Moduli spaces of Riemann surfaces and symmetric products: A combinatorial description of the Mumford–Miller–Morita classes

    This is my master thesis which was finished in the summer term 2018 under the supervision of Carl-Friedrich Bödigheimer. Its main result is a Poincaré–Lefschetz correspondence between the Mumford–Miller–Morita classes in the cohomology of moduli spaces and certain subcomplexes of Bödigheimer’s simplicial model of parallel slit domains.


Teaching

In the summer term 2022, I am the teaching assistant for the lectures Einführung in die Geometrie und Topologie by Koen van den Dungen and Topology 2 by Daniel Kasprowski.

In the summer term 2020, I co-organised a graduate seminar on Operads in Algebra and Topology together with Andrea Bianchi. Moreover, I have been tutor for the following topology lectures:

SoSe 2021 Algebraic Topology 2Carl-Friedrich Bödigheimer
WiSe 2020/21Algebraic Topology 1Carl-Friedrich Bödigheimer
SoSe 2020 Algebraic Topology 2Christoph Winges
WiSe 2019/20Algebraic Topology 1Wolfgang Lück
SoSe 2019 Topology 2Daniel Kasprowski
WiSe 2018/19Topology 1Wolfgang Lück
SoSe 2018 Einführung in die Geometrie und TopologieWolfgang Lück

News


18./19. october: Symposium of the Global Math Network

Plücker Lectures Kevin Buzzard & Johan Commelin 3-8 November

Prof. Ana Caraiani wins a New Horizons in Mathematics Prizes 2023

17. Oktober 2022: Vorstellung der Hirzebruch-Sammlung und Auftaktveranstaltung des Otto Toeplitz-Gedächtnisstiftungsfonds

Pius XI Medal awarded to Professor Peter Scholze

Prof. Dr. Ana Caraiani neuer Hausdorff Chair am Mathematischen Institut

Prof. Valentin Blomer und Prof. Georg Oberdieck erhalten ERC grants

Prof. Peter Scholze erhält Lehrpreis der Universität

Ausschreibung: W3-Professur Reine Mathematik

Bonn Mathematics ranked 15th in Shanghai Ranking

Prof. Carl-Friedrich Bödigheimer hat Daidalos-Münze der Studienstiftung erhalten

Teaching prize of the Faculty of Mathematics and Natural Sciences 2021 is awarded to Prof. Valentin Blomer

Grants for Mathematics students from Ukraine

Attack on Ukraine

Corona: Measures at the Center for Mathematics

Prof. Jessica Fintzen is awarded a Whitehead Prize of the London Mathematical Society

Georg Oberdieck receives Dubrovin Medal 2022

Prof. Peter Scholze elected as Foreign Member of the Royal Society

Prof. Dr. Jessica Fintzen new at the Mathematical Institute

Otto Toeplitz memorial fund established

Prof. Catharina Stroppel invited as plenary speaker to the ICM 2022 in St. Petersburg

Bonner Mathematik belegt bei Shanghai Ranking den 1. Platz in Deutschland und weltweit den 13. Platz

Prof. Georg Oberdieck erhält Heinz Maier-Leibnitz-Preise 2020

Prof. Daniel Huybrechts erhält gemeinsam mit Debarre, Macri und Voisin ERC Synergy Grant