Group Theory and Friends | Berlin Math Seminars

Group Theory and Friends 📅

Homepage

https://sites.google.com/view/grouptheoryandfriends/home

Institute

TU Berlin

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

roughly every second week (day/time vary by talk)

Usual venue

NOT_SET

Number of talks

Comment

Irregular scheduling: the seminar meets roughly every second week, with day of week and start time varying by talk and semester. The location also varies by talk; many meetings are in MA 366, but MA 650 and ER 164 also appear. The page may list related external events (e.g., EGGG, MATH+ colloquium); these are not series defaults.

Group Theory

Tue, 28.04.26 at 14:00

MA 366

Simon Andre Paris

On the Tarski problem for hyperbolic groups in the presence of torsion

Abstract.

Following his resolution of a famous problem of Tarski concerning elementary equivalence of non-abelian free groups, Sela gave a complete classification of torsion-free hyperbolic groups up to elementary equivalence. I will recall the necessary definitions, outline Sela's classification and explain some of the new difficulties encountered when elements of finite order are allowed, in particular the existence of pathological morphisms from surface groups to hyperbolic groups with torsion.

Group Theory

Tue, 21.04.26 at 14:00

MA 366

Corentin Bodart Oxford

Subgroup membership and formal languages

Abstract.

The intersection of Geometric Group Theory and Formal Language Theory has been fruitful in the last 50 years. I'll start by recalling some of the key results in the area, such as the Muller-Schupp theorem on groups with context-free Word Problem and Lehnert's conjecture on groups with co-context-free Word Problem. In joint work with André Carvalho and Carl-Fredrik Nyberg-Brodda, we have been looking at similar languages related to another decision problem in groups: Subgroup Membership. I'll explain the toolbox we have been developing, apply it to examples and non-examples, and highlight some open problems along the way.

Group Theory

Wed, 21.01.26 at 14:00

MA 366

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.

Group Theory

Wed, 14.01.26 at 14:00

MA 366

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.

Group Theory

Wed, 10.12.25 at 14:30

ER 164

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.

Group Theory

Wed, 12.11.25 at 14:00

MA 650

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.

Group Theory

Wed, 29.10.25 at 14:30

MA 650

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.

Group Theory

Wed, 29.10.25 at 13:45

MA 366

Tamara Imanuel

Das Konjugationsproblem in RAAGs: Theorie und Algorithmus

Group Theory

Wed, 22.10.25 at 14:30

MA 650

Sobhi Massalha TUB

Sentences over Random Groups

Abstract.

Around 2013, a natural conjecture by Julia Knight anticipated that given a first order sentence, its truth value over a random group in the few relators model, is equivalent to its truth value over non-abelian free groups. Our work extends the framework of this conjecture to random groups in the Gromov Density Model, at optimal density d<1/2. We prove the conjecture for sentences that belong to the Boolean algebra of universal sentences, as well as for sentences of minimal rank with arbitrary number of quantifiers, for random groups of density d<1/2. In this talk, we will present our results and, as time permits, outline the key strategies and ideas involved in the proofs.

Group Theory

Wed, 08.10.25 at 10:45

MA 366

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.

Group Theory

Wed, 08.10.25 at 10:00

MA 366

Nico Waldau TU Berlin

Tits-Alternative für hyperbolische Gruppen

Group Theory

Tue, 21.01.25 at 14:30

TU Berlin, MA Bui...

Jan Moritz Petschick Uni Bielefeld