Browsing 1 - Oberwolfach Preprints (OWP) by MSC "20"
Now showing items 1-20 of 44
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The Brown Complex in Non-Defining Characteristic and Applications
[OWP-2023-14] (Mathematisches Forschungsinstitut Oberwolfach, 2023-07-25)We study the Brown complex associated to the poset of $\ell$-subgroups in the case of a finite reductive group defined over a field $\mathbb{F}_q$ of characteristic prime to $\ell$. First, under suitable hypotheses, we ... -
Calculating conjugacy classes in Sylow p-subgroups of finite Chevalley groups of rank six and seven
[OWP-2013-10] (Mathematisches Forschungsinstitut Oberwolfach, 2013-04-10)Let $G(q)$ be a finite Chevalley group, where $q$ is a power of a good prime $p$, and let $U(q)$ be a Sylow $p$-subgroup of $G(q)$. Then a generalized version of a conjecture of Higman asserts that the number $k(U(q))$ of ... -
Cataland: Why the Fuß?
[OWP-2019-01] (Mathematisches Forschungsinstitut Oberwolfach, 2019-01-21)The three main objects in noncrossing Catalan combinatorics associated to a finite Coxeter system are noncrossing partitions, clusters, and sortable elements. The first two of these have known Fuß-Catalan generalizations. ... -
Categoric Aspects of Authentication
[OWP-2012-05] (Mathematisches Forschungsinstitut Oberwolfach, 2012-04-24) -
The Character Triple Conjecture for Maximal Defect Characters and the Prime 2
[OWP-2023-15] (Mathematisches Forschungsinstitut Oberwolfach, 2023-08-22)We prove that Späth’s Character Triple Conjecture holds for every finite group with respect to maximal defect characters at the prime 2. This is done by reducing the maximal defect case of the conjecture to the so-called ... -
Cocharacter-closure and spherical buildings
[OWP-2015-12] (Mathematisches Forschungsinstitut Oberwolfach, 2015-07-29)Let $k$ be a field, let $G$ be a reductive $k$-group and $V$ an affine $k$-variety on which $G$ acts. In this note we continue our study of the notion of cocharacter-closed $G(k)$-orbits in $V$. In earlier work we used a ... -
Cocharacter-Closure and the Rational Hilbert-Mumford Theorem
[OWP-2014-16] (Mathematisches Forschungsinstitut Oberwolfach, 2014-12-20)For a field $k$, let $G$ be a reductive $k$-group and $V$ an affine $k$-variety on which $G$ acts. Using the notion of cocharacter-closed $G(k)$-orbits in $V$ , we prove a rational version of the celebrated Hilbert-Mumford ... -
Computing Congruence Quotients of Zariski Dense Subgroups
[OWP-2018-22] (Mathematisches Forschungsinstitut Oberwolfach, 2018-10-26)We obtain a computational realization of the strong approximation theorem. That is, we develop algorithms to compute all congruence quotients modulo rational primes of a finitely generated Zariski dense group $H \leq ... -
Congruences Associated with Families of Nilpotent Subgroups and a Theorem of Hirsch
[OWP-2019-16] (Mathematisches Forschungsinstitut Oberwolfach, 2019-05-27)Our main result associates a family of congruences with each suitable system of nilpotent subgroups of a finite group. Using this result, we complete and correct the proof of a theorem of Hirsch concerning the class number ... -
A construction of hyperbolic Coxeter groups
[OWP-2010-04] (Mathematisches Forschungsinstitut Oberwolfach, 2010)We give a simple construction of Gromov hyperbolic Coxeter groups of arbitrarily large virtual cohomological dimension. Our construction provides new examples of such groups. Using this one can construct e.g. new groups ... -
Deciding Non-Freeness of Rational Möbius Groups
[OWP-2022-07] (Mathematisches Forschungsinstitut Oberwolfach, 2022-03-22)We explore a new computational approach to a classical problem: certifying non-freeness of (2-generator, parabolic) Möbius subgroups of SL(2, $\mathbb{Q}$). The main tools used are algorithms for Zariski dense groups and ... -
Edifices: Building-like Spaces Associated to Linear Algebraic Groups; In memory of Jacques Tits
[OWP-2023-04] (Mathematisches Forschungsinstitut Oberwolfach, 2023-06-19)Given a semisimple linear algebraic $k$-group $G$, one has a spherical building $Δ_G$, and one can interpret the geometric realisation $Δ_G(\mathbb R)$ of $Δ_G$ in terms of cocharacters of $G$. The aim of this paper is to ... -
Embedding Spaces of Split Links
[OWP-2022-13] (Mathematisches Forschungsinstitut Oberwolfach, 2022-08-01)We study the homotopy type of the space $\mathcal{E}(L)$ of unparametrised embeddings of a split link $L=L_1\sqcup \ldots \sqcup L_n$ in $\mathbb{R}^3$. Inspired by work of Brendle and Hatcher, we introduce a semi-simplicial ... -
Experimenting with Symplectic Hypergeometric Monodromy Groups
[OWP-2019-15] (Mathematisches Forschungsinstitut Oberwolfach, 2019-05-22)We present new computational results for symplectic monodromy groups of hypergeometric differential equations. In particular, we compute the arithmetic closure of each group, sometimes justifying arithmeticity. The results ... -
Experimenting with Zariski Dense Subgroups
[OWP-2017-31] (Mathematisches Forschungsinstitut Oberwolfach, 2017-10-28)We give a method to describe all congruence images of a finitely generated Zariski dense group $H\leq SL(n, \mathbb{R})$. The method is applied to obtain efficient algorithms for solving this problem in odd prime degree ... -
Flag-Accurate Arrangements
[OWP-2023-01] (Mathematisches Forschungsinstitut Oberwolfach, 2023-02-13)In [MR21], the first two authors introduced the notion of an accurate arrangement, a particular notion of freeness. In this paper, we consider a special subclass, where the property of accuracy stems from a flag of flats ... -
Freeness of Multi-Reflection Arrangements via Primitive Vector Fields
[OWP-2017-10] (Mathematisches Forschungsinstitut Oberwolfach, 2017-04-20)In 2002, Terao showed that every reflection multi-arrangement of a real reflection group with constant multiplicity is free by providing a basis of the module of derivations. We first generalize Terao's result to ... -
G-complete reducibility in non-connected groups
[OWP-2013-09] (Mathematisches Forschungsinstitut Oberwolfach, 2013-04-10)In this paper we present an algorithm for determining whether a subgroup $H$ of a non-connected reductive group $G$ is $G$-completely reducible. The algorithm consists of a series of reductions; at each step, we perform ... -
Ghost Algebras of Double Burnside Algebras via Schur Functors
[OWP-2012-09] (Mathematisches Forschungsinstitut Oberwolfach, 2012-07-03)For a finite group $G$, we introduce a multiplication on the $\mathbb{Q}$-vector space with basis $\mathscr{S}_{G\times G}$, the set of subgroups of ${G \times G}$. The resulting $\mathbb{Q}$-algebra $\tilde{A}$ can be ... -
Group-Graded Rings Satisfying the Strong Rank Condition
[OWP-2019-22] (Mathematisches Forschungsinstitut Oberwolfach, 2019-08-16)A ring $R$ satisfies the $\textit{strong rank condition}$ (SRC) if, for every natural number $n$, the free $R$-submodules of $R^n$ all have rank $\leq n$. Let $G$ be a group and $R$ a ring strongly graded by $G$ such that ...