Simon
Andre
Paris
Group Theory and Friends  📅
Institute
Head
Laura Ciobanu
Organizer
Laura Ciobanu
Description
This seminar is organized by the Applied Algebra Group at TU Berlin. It covers topics in group theory and related areas.
Usual time
Wednesdays at 14:30 (biweekly)
Usual venue
TU Berlin, MA Building
Number of talks
11
April 2026
Corentin
Bodart
Oxford
January 2026
Jan Moritz
Petschick
Uni Bielefeld
Maximal subgroups in branch groups
Abstract.
Branch groups are groups whose subgroup structure resembles a rooted tree. Among many other intriguing properties, they contain examples of groups with unusual restrictions on their maximal subgroups. In this talk, I will provide an account of what is known about maximal subgroups of branch groups and present some recent results.
Matthew
Konefal
Loughborough, UK
Definability in Theories Based on Free Group and Free Monoid Equations
Abstract.
Equations in the free group and free monoid have long been studied together. I’ll outline their history and properties, comparing facets of their two theories. Each can be studied by adapting techniques developed for the other. After demonstrating this, we’ll focus on definability in theories whose atoms are free group equations. Tools for establishing nondefinability in this setting are due to group theorists and model theorists, yet have the appearance of word-combinatorial lemmas. The tools - combined - yield characterisations of definability, the free monoid analogues of which seem more elusive. I'll end discussing length abstractions and length constraints, which link equations to weak arithmetics. Naturally, more definability questions result, including major open problems.
December 2025
Leon
Pernak
Uni Saarland
Quadratic equations in wreath products of abelian groups
Abstract.
One of the strongest results that one can hope for when studying decidability questions in groups is the decidability of equations - is there an algorithm that, if we feed it a group equation, tells us if the equation has or does not have a solution in a given group? I will discuss this problem in the setting of wreath products of abelian groups. In particular, I will explain how to prove that the problem is decidable for quadratic equations, using techniques and intuitions inspired by commutative algebra. This is joint work with Ruiwen Dong and Jan-Philipp Wächter.
November 2025
Kevin
Li
FU Berlin
On higher coherence of RAAGs
Abstract.
A group is called coherent if every finitely generated subgroup is finitely presented. It is a classical result of Droms that a RAAG is coherent if and only if the defining graph is chordal. I will explain its proof and our attempt to generalise it to higher coherence. Ongoing joint work with Luis Jorge Sánchez Saldaña.
October 2025
Mireille
Soergel
TUB
Dual Artin groups
Abstract.
In 1998 when considering a new approach to the word and conjugacy problem in Braid groups, Birman-Ko-Lee introduce a new presentation for the braid group. This is now referred to as the dual presentation. Such dual presentations can be defined for all Artin groups. I will introduce standard and dual Artin groups and talk about some open conjectures.
Tamara
Imanuel
Das Konjugationsproblem in RAAGs: Theorie und Algorithmus
Alex
Levine
University of East Anglia
The Diophantine problem in Thompson's group F
Abstract.
We discuss equations in groups, and when there exists an algorithm that can decide if a given system of equations admits a solution. We mention some recent work on Thompson's groups F and T. Based on joint work with Luna Elliott.
Nico
Waldau
TU Berlin
Tits-Alternative für hyperbolische Gruppen
January 2025
Jan Moritz
Petschick
Uni Bielefeld