arXiv subjects

Frederik Caenepeel

Publications and source records attributed to Frederik Caenepeel.

7 recordsLinked to original sources

arXiv2020

Glider Representation Rings with a view on distinguishing groups

Let $G$ be a finite group. In the first part of the paper we develop further the foundations of the youngly introduced glider representation theory. Glider representations encompass filtered modules over filtered rings and as such carry much information of $G$. Therefore the main focus is on the glider representation ring $R_d(\widetilde{G})$, which is shown to be realisable as a concrete subring of the split Grothendieck ring of the monoidal category $\text{glid}_d(G)$ of (Noetherian) glider $\mathbb{C}$-representations of (length $d$) of $G$. In the second part we investigate a Wedderburn-Malcev type decomposition of the (infinite-dimensional) $\mathbb{Q}$-algebra $\mathbb{Q}(\widetilde{G}) := \mathbb{Q} \otimes_{\mathbb{Z}}R_1(\widetilde{G})$. The main theorem obtains a $\mathbb{Q}[G^{ab}]$-module decomposition of $\mathbb{Q}(\widetilde{G})$ relating it in a precise way to $\mathbb{C}$-representation theory of subnormal subgroups in $G$. Under certain vanishing assumptions, which are proven to hold for nilpotent groups (of class $2$), the second main theorem completely describes a $\mathbb{Q}[G^{ab}]$-algebra decomposition. We end with pointing out applications on distinguishing isocategorical groups.

math.RT↗

arXiv2019

Glider representations of group algebra filtrations of nilpotent groups

We continue the study of glider representations of finite groups $G$ with given structure chain of subgroups $e \subset G_1 \subset \ldots \subset G_d = G$. We give a characterization of irreducible gliders of essential length $e \leq d$ which in the case of $p$-groups allows to prove some results about classical representation theory. The paper also contains an introduction to generalized character theory for glider representations and an extension of the decomposition groups in the Clifford theory. Furthermore, we study irreducible glider representations for finite nilpotent groups.

math.RT↗

arXiv2019

Glider Brauer-Severi varietes of central simple algebras

The glider Brauer-Severy variety GBS(A) of a central simple algebra A over a field K is introduced as the set of all irreducible left glider ideals in A for some filtration FA. For fields we deduce that GBS(K) equals R(K) x Z, the product of the Riemann surface of K and the ring of integers Z. For a csa A over K it turns out that GBS(A) = BS(A) x GBS(K), where BS(A) denotes the classical Brauer-Severi variety of A.

math.RA↗

arXiv2018

Generalized characters for glider representations of groups

Glider representations can be defined for a finite algebra filtration FKG determined by a chain of subgroups 1 < G_1 < ... < G_d = G. In this paper we develop the generalized character theory for such glider representations. We give the generalization of Artin's theorem and define a generalized inproduct. For finite abelian groups G with chain 1 < G, we explicitly calculate the generalized character ring and compute its semisimple quotient. The papers ends with a discussion of the quaternion group as a first non-abelian example.

math.GR↗

arXiv2017

Glider representations of chains of semisimple Lie algebras

We start the study of glider representations in the setting of semisimple Lie algebras. A glider representation is defined for some positively filtered ring $FR$ and here we consider the right bounded algebra filtration $FU(\mathfrak{g})$ on the universal enveloping algebra $U(\mathfrak{g})$ of some semisimple Lie algebra $\mathfrak{g}$ given by a fixed chain of semisimple sub Lie algebras $\mathfrak{g}_1 \subset \mathfrak{g}_2 \subset \ldots \subset \mathfrak{g}_n = \mathfrak{g}$. Inspired by the classical representation theory, we introduce so-called Verma glider representations. Their existence is related to the relations between the root systems of the appearing Lie algebras $\mathfrak{g}_i$. In particular, we consider chains of simple Lie algebras of the same type $A,B,C$ and $D$.

math.RT↗

arXiv2016

Clifford theory for glider representations

Classical Clifford theory studies the decomposition of simple $G$-modules into simple $H$-modules for some normal subgroup $H \triangleleft G$. In this paper we deal with chains of normal subgroups $1 \triangleleft G_1 \triangleleft \cdots \triangleleft G_d =G$, which allow to consider fragments and in particular glider representations. These are given by a descending chain of vector spaces over some field $K$ and relate different representations of the groups appearing in the chain. Picking some normal subgroup $H \triangleleft G$ one obtains a normal subchain and one can construct an induced fragment structure. Moreover, a notion of irreducibility of fragments is introduced, which completes the list of ingredients to perform a Clifford theory.

math.RT↗

arXiv2016

Localization and sheaves of glider representations

The notion of a glider representation of a chain of normal subgroups of a group is defined by a new structure, i.e. a fragment for a suitable filtration on the group ring. This is a special case of general glider representations defined for a positively filtered ring $R$ with filtration $FR$ and subring $S = F_0R$. Nice examples appear for chains of groups, chains of Lie algebras, rings of differential operators on some variety or $V$-gliders for $W$ for algebraic varieties $V$ and $W$. This paper aims to develop a scheme theory for glider representations via the localizations of filtered modules. With an eye to noncommutative geometry we allow schemes over noncommutative rings with particular attention to so-called almost commutative rings. We consider particular cases of $\mathrm{Proj}~ R$ (e.g. for some P.I. ring $R$) in terms of prime ideals, $R$-tors in terms of torsion theories and $\underline{\mathcal{W}}(R)$ in terms of a noncommutative Grothendieck topology based on words of Ore set localizations.

math.RA↗