Numerical semigroups are the subsemigroups of the set of natural numbers that are cofinite and contain $0$. Let $S$ be a numerical semigroup and $c$ be the smallest number such that $S$ is the union of a finite subset of $[0,c]$ and the integer interval $[c,\infty)$. Wilf's conjecture states that the density of elements of $S$ in the interval $[0,c]$ is at least equal to $1/d$, where $d$ is the dimension of the numerical semigroup $S$.

The classification of tuples of matrices up to simultaneous conjugation is a classical problem in linear algebra and representation theory. While the case of a single matrix leads to the well-known Jordan normal form, the situation becomes far more intricate for tuples, where the problem is considered "wild" and therefore not classifiable in any reasonable sense. Geometric Invariant Theory (GIT) provides a powerful framework for studying such spaces through quotient varieties, which parametrize semisimple representations of free associative algebras.

A numerical semigroup $S$ is a cofinite submonoid of the aditive monoid $(\mathbb{N},+)$. The (finite) complement of $S$ in $\mathbb{N}$ is the genus of $S$.

I plan to recall a well-known process of exploring the classical numerical semigroups tree as a means to count numerical semigroups by genus. The process is easily adapted to verify properties: one verifies the property at each explored node.

How much does the universal enveloping algebra of a Lie algebra remember about the Lie algebra itself? This is the statement of a classical problem in algebra called ``the isomorphism problem for enveloping algebras". In this talk, I'll explain how modern tools from algebraic homotopy theory and deformation theory allow us to make new progress on this problem. Along the way, we'll see that this is closely related to the following intriguing question: in the realm of homotopy theory, is being a commutative algebra simply a property, or is it an additional structure?

In this talk, we will present the bijective correspondence between Young diagrams and proper numerical sets. Then we will use this correspondence to introduce Young diagram decompositions for symmetric numerical sets (and semigroups). We will extend these decompositions to almost symmetric numerical semigroups.

There will be a coffee break after the seminar. 

References

In this talk we present some properties of generalized torsion elements in groups. We describe the set of generalized torsion elements in finitely generated abelian-by-finite groups. In addition, we present a family of Bieberbach groups in which every element is a generalized torsion element. This presentation is mainly based in the following papers [1,2,3]. 

There will be a coffee break after the seminar.

References

[1] R. Bastos and L. Mendonça. Generalized torsion elements in infinite groups. arXiv:2411.17918 [math.GR]. 

This presentation is based on joint work with P. Shumyatsky. We study the class of all finite groups in which every commutator has prime power order. A group in this class is called a CPPO-group. Our interest in this class arose from the observation that it includes, as a subclass, all finite groups in which every element has prime power order - commonly known as EPPO-groups. These were the subject of foundational work by G. Higman and M.

Quasi-Frobenius rings were introduced by Nakayama  in the study of representations of algebras. Afterwards, Quasi-Frobenius rings played a central role in ring theory, and numerous characterizations were given by various authors. In particular, Ikeda characterized these rings as two sided self-injective and two sided Artinian.

The main objective of multiplicative ideal theory is to investigate the multiplicative structure of integral domains by means of ideals or certain systems of ideals of that domain. An essential tool in multiplicative ideal theory is the concept of  ``star operation"  which was introduced by Krull in 1936 and then was used by Gilmer in his book in 1972. In this talk, we first introduce some concepts related to multiplicative ideal theory. The emphasis will be given to the ``$w$-operation", one of the most important star operations.

In the previous talk, we revisited some general aspects of the representation theory of the Lie algebra $\mathrm{gl}(n)$ and used them as motivation to study Gelfand-Tsetlin modules via Drinfeld categories. In this seminar, we will take a step back to build a solid foundation before diving into Gelfand-Tsetlin modules. We will start by recalling key results from the classical representation theory of $\mathrm{sl}(2)$, ensuring that we have the necessary tools and intuition. With this groundwork in place, we will then explore how Gelfand-Tsetlin modules appear in this setting.