Organisatoren: Dr. Niamh Farrell, Jun.-Prof. Dr. Caroline Lassueur und  Lucas Ruhstorfer

Termin: Donnerstags 17:00-18:00, Raum 48-436

• Dienstag, 15. Oktober 2019: A Day of Representation Theory at the Villa Denis 2019
  • Olivier Dudas (Paris VII): Unitriangular shape of decomposition matrices of unipotent blocks
  • Emily Norton (Gast TU Kaiserslautern): Harish-Chandra series of unipotent representations of finite unitary groups
  • Noelia Rizo Carrión (Università degli Studi di Firenze): Galois action on the principal block
  • Lucas Ruhstorfer (TU Kaiserslautern): Jordan decomposition for the Alperin-McKay conjecture

• Donnerstag, 31. Oktober 2019: Julian Brough (Bergische Universität Wuppertal)
  
  • Titel: A criterion for the inductive Alperin weight condition [Abstract]
    
    Many of the local-global conjectures have been reduced to so called inductive conditions on simple groups. Moreover Späth has been successful in verifying the inductive McKay condition for most families of simple groups by considering an alternative criterion on a larger group with some additional information about the corresponding Clifford theory. In this talk I will discuss a joint work with Späth, in which we have provided an analogous criterion for the Alperin weight conjecture.
    
    

• Donnerstag, 7. November 2019: Paul Wedrich (MPI Bonn)
  
  • Titel: Quivers for SL(2) tilting modules [Abstract]
    
    I will explain how diagrammatic algebra can be used to give an explicit generators-and-relations presentation of all morphisms between indecomposable tilting modules for SL(2) over an algebraically closed field of positive characteristic. The result takes the form of a path algebra of an infinite, fractal-like quiver with relations, which can be considered as the (semi-infinite) Ringel dual of SL(2). Joint work with Daniel Tubbenhauer.
    
    

• Donnerstag, 14. November 2019: kein Seminar

• Donnerstag, 21. November 2019: Jens Eberhardt (UCLA, Bonn)
  
  • Titel: Motives in Geometric Representation Theory [Abstract]
    
    Categories of representations arising in Lie theory can often be modeled geometrically in terms of constructible sheaves on certain spaces, as for example on the flag variety, affine Grassmannian or the nilpotent cone. Recent developments in the theory of motives allow to consider so called "motivic sheaves", an algebro-geometric analogue of constructible sheaves. In this talk we will explain how one can practically work with motivic sheaves (using Grothendieck's six functor formalism) and apply them in representation theory. We will show how motivic sheaves can be used to model Category O associated to a reductive complex Lie algebra, modular Category O associated to a split reductive group over a finite field and categories of representations of convolution algebras, such as the graded affine Hecke algebra and KLR-algebras. We also will explain how more "exotic" versions of motivic sheaves provide exciting new opportunities in geometric representation theory.
    
    

• Donnerstag, 28. November 2019: Ivo Dell'Ambrogio (Université de Lille)
  
  • Titel: The Green correspondence in algebra and topology [Abstract]
    
    The Green correspondence, a classic and basic result of modular representation theory, describes a bijection between indecomposable H-modules and indecomposable G-modules having the same vertex Q, provided H is a subgroup of G containing the normaliser of Q. Already in the 70's, Green himself noticed that the correspondence can be strengthened to an equivalence of categories between certain additive sub-quotients of G-modules and H-modules. I will explain how the latter Green equivalence can be proved and clarified in the general setting of "Mackey 2-functors", and how one can make sense of it also in situations where the Krull-Schmidt theorem does not hold (where indecomposable objects are not helpful). For example, and perhaps most notably, there follows a version of the Green equivalence for equivariant stable homotopy theory. This is joint work with Paul Balmer.
    
    

• Donnerstag, 5. Dezember 2019: kein Seminar (Nikolaus Conference)

• Donnerstag, 12. Dezember 2019: kein Seminar (Konferenz: Women in Algebra and Symbolic Computations)

• Donnerstag, 19. Dezember 2019: Ellen Henke (University of Aberdeen)
  
  • Titel: A generalisation of a theorem by Camina-Herzog [Abstract]
    
    An old theorem of Camina—Herzog states that a finite group has abelian Sylow 2-subgroups if the centralizer of any 2-element is of odd index. After an introduction to the theory of fusion systems, I will present a generalization of this theorem to fusion systems together with a very short and elementary proof. As a corollary, one obtains a theorem about 2-blocks of finite groups which was conjectured by Külshammer, Sambale and Tiep.
    
    

• Donnerstag, 9. Januar 2020: kein Seminar

• Donnerstag, 16. Januar 2020: kein Seminar (canceled)

• Donnerstag, 23. Januar 2020: Jenny August (MPI Bonn)
  
  • Titel: Contraction Algebras in the Homological Minimal Model Programme [Abstract]
    
    In this talk, I will give an introduction to a class of symmetric, finite dimensional algebras, known as contraction algebras, which are one of the main tools used in the Homological Minimal Model Programme. This program aims to use noncommutative algebra to answer questions in algebraic geometry and my goal for the talk is to not only convince you that the contraction algebras are very useful for this purpose, but to also show you that they have some very interesting algebraic properties.
    
    

• Donnerstag, 30. Januar 2020: Vincent Beck (Université de Tours/ Université d'Orléans)
  • Titel: Cohomological computations for reflection groups and their braid groups and application to the determination of the finite subgroups of B/[P,P] [Abstract]
    
    In 2015, Guaschi, Goncalves and Ocampos started to study the finite subgroups of $B_n/[P_n,P_n]$ where $B_n$ is the standard braid group on $n$ strands and $P_n$ the pure braid group. They exhibited cyclic and abelian subgroup and even a non abelian subgroup of $B_7/[P_7,P_7]$. Their constructions were generalized to complex reflection groups by Marin. Finally, using cohomological methods, in a joint work with Marin, we were able to give a complete description of the finite subgroups of $B/[P,P]$ for every complex reflection groups $W$ (where $B$ is the braid group of $W$ and $P$ its pure braid group). I will present these results and how the cohomological description of the exact sequence 1-> P/[P,P] -> B/[P,P] -> W -> 1 has led to our classification of finite subgroups of B/[P,P].
    
    

• Donnerstag, 6. Februar 2020: Maike Gruchot (RWTH Aachen)
  • Titel: On a relative version of complete reducibility [Abstract]
    
    In this talk we discuss a relative version of Serre’s notion of complete reducibility introduced by Bate, Martin, Röhrle and Rudolf. In the first part of the talk I introduce Serre’s notion of complete reducibility. In the second part, we introduce the relative version and discuss a characterization of relative G-complete reducibility which directly generalizes equivalent formulations of complete reducibility in representation theory. In the last part of the talk, we consider the case of a subgroup of G which normalizes the identity component K^0 of K, it turns that such a subgroup is relatively G-completely reducible with respect to K if and only if its image in the automorphism group of K^0 is completely reducible. This allows us to generalize a number of fundamental results from the absolute to the relative setting.
    
    

• Donnerstag, 13. Februar 2020: kein Seminar

Organisatoren: Dr. Niamh Farrell  und Dr. Alessandro Paolini

Termin: Donnerstags 17:00-18:00, Raum 48-436

• Montag(!), 15. April 2019, 15:45 Uhr: Bernhard Böhmler [TU Kaiserslautern]
  • Titel: On a counter-example to a conjecture about Morita algebras [Abstract]
  
  This is joint work with René Marczinzik. We give an example of a Morita algebra A with a tilting module T such that the endomorphism algebra End(T) over A has dominant dimension at least two, but is not a Morita algebra. This provides a counter-example to a conjecture by Hongxing Chen and Changchang Xi.
  
  

• Donnerstag, 25. April 2019: Sophiane Yahiatene [Universität Bielefeld]
  • Titel: Hurwitz action and extended Weyl groups [Abstract]
  
  In the talk we will investigate the so-called extended Weyl groups which can be seen as a extention of a family of Coxeter groups. In these groups we will consider a class of distinguished elements, called Coxeter transformations and define a group action on certain factorizations of them. The action is called Hurwitz action and appears in the study of hereditary abelian categories. It serves as a helpful tool in understanding the lattice of thick subcategories. (j.w. B. Baumeister and P. Wegener)
  
  

• Donnerstag, 2. Mai 2019: Jonas Hetz [Universität Stuttgart]
  • Titel: On the values of unipotent characters of finite groups of Lie type [Abstract]

• Donnerstag, 9. Mai 2019: Martin Hofer [LMU München]
  • Titel: Construction of elliptic p-units [Abstract]
  
  Special values of elliptic functions have been studied since the 19th century, an example being the elliptic units defined by G. Robert in the 1970s. Interest in elliptic units has reemerged in the more recent past as they have proven to be quite useful in Iwasawa theory in cases where the base field k is imaginary quadratic. In this talk we present a construction of certain p-units with the help of classical elliptic units and compute their valuation when a rational prime p is non-split in k. This result, which can be used in Iwasawa theory, is an extension of the work done in the split case by W. Bley and a natural analogue of the cyclotomic situation proved by D. Solomon. In particular, we want to present how we collected numerical evidence for our theorem before proving it. Most parts of this project are joint work with W. Bley.
  
  

• Donnerstag, 16. Mai 2019: Kein Seminar.

• Donnerstag, 23. Mai 2019: Patrick Wegener [TU Kaiserslautern]
  • Titel: An invitation to Coxeter and Artin groups [Abstract]
  
  In this talk I will shortly review the definitions of Coxeter and Artin groups. Then I will explain and state some of the open problems and open conjectures in the theory of Coxeter and Artin groups. Furthermore I will explain how some of my results and my research are (or might be) related to these problems and conjectures.
  
  

• Donnerstag, 30. Mai 2019: Kein Seminar (Christi Himmelfahrt).

• Donnerstag, 6. Juni 2019: Thomas Weigel [Universita' di Milano-Bicocca] CANCELED!
  
  • Titel: tba

• Donnerstag, 13. Juni 2019: Kein Seminar (Konferenz: Groups, Rings and Associated Structures 2019 in Spa).

• Donnerstag, 20. Juni 2019: Kein Seminar (Fronleichnam).

• Montag, 24. Juni 2019: Michael Livesey [Universität Jena]
  • Titel: On Donovan's conjecture for abelian defect groups and strong Frobenius numbers [Abstract]
  
  Donovan's conjecture states that for a fixed p-group P there are only finitely many blocks (up to Morita equivalence) with defect group isomorphic to P. In this talk I will talk about recent progress made on this question for P abelian. The main tool used is the strong Frobenius number of a block. I will also talk about the corresponding results over an appropriately defined complete, discrete valuation ring. This is joint work with Charles Eaton and Florian Eisele.
  
  

• Donnerstag, 27. Juni 2019: Giovanni De Franceschi [University of Auckland]
  • Titel: Centralizers and conjugacy classes in finite classical groups [Abstract]
  
  In computational group theory, solving problems on finite simple groups allows to solve problems in general, since there is plenty of literature on how to extend solutions to extensions of groups and products of groups. Groups of matrices are one of the best known classes of finite simple groups, so studying classical groups (groups of isometries for non-degenerate forms on vector spaces) is the first step to get solutions of many problems. In this talk I show three strictly correlated problems: list conjugacy classes, describe explicitely a conjugacy element, describe the group structure of the centralizer of an arbitrary element. During my PhD at University of Auckland I integrated the pre-existing results for some particular cases and extended them to subgroups of isometry groups (special and Omega groups). I will also show the results of the algorithmic study run parallel to the theoretical research.
  
  

• Donnerstag, 4. Juli 2019: Eugenio Giannelli [Università degli Studi di Firenze]
  • Titel: Character correspondences for symmetric and complex reflection groups [Abstract]

• Montag, 8. Juli 2019, 15:30 (Raum 48-438): Shigeo Koshitani [Chiba University]
  • Title: Equivalences of blocks algebras
  
  Donovan's conjecture states that for a fixed p-group P there are only finitely many blocks (up to Morita equivalence) with defect group isomorphic to P. In this talk I will talk about recent progress made on this question for P abelian. The main tool used is the strong Frobenius number of a block. I will also talk about the corresponding results over an appropriately defined complete, discrete valuation ring. This is joint work with Charles Eaton and Florian Eisele.
  
  

• Donnerstag, 11. Juli 2019, 16:15-17:15 (!): Leo Margolis [Vrije Universiteit Brussel]
  • Titel: Blocks of defect 1 and units in integral group rings [Abstract]

• Donnerstag, 18. Juli 2019: Vortrag im Oberseminar

Organisatoren: Dr. Niamh Farrell  und Dr. Alessandro Paolini

Termin: Donnerstags 17:15-18:15, Raum 48-436

• Donnerstag, 25. Oktober 2018: Melissa Lee [Imperial College London],
  •  Titel: Bases of almost quasisimple groups and Pyber's conjecture [Abstract]

• Donnerstag, 1. November 2018: Kein Seminar (Allerheiligen)

• Donnerstag, 8. November 2018: Yann Palu [LAMFA, Amiens]
  
  • Titel: From cluster algebras to cluster categories [Abstract]
    
    The classification of cluster algebras with finitely many clusters shares some similarities with Gabriel's theorem on the classification of finite dimensional algebras (or quivers) of finite representation type. The link between cluster algebras and representation theory of quivers, first studied by Marsh-Reineke-Zelevinsky, was made more precise by Buan-Marsh-Reineke-Reiten-Todorov (see also Caldero-Chapoton-Schiffler for type A) by using the so-called cluster categories. This talk will be an introduction to the representation theory of quivers and to cluster categories. We will mainly focus on the example of quivers of Dynkin type A.
    
    

• Donnerstag, 15. November 2018: Stacey Law [University of Cambridge]
  • Titel: Linear characters of Sylow subgroups of the symmetric group [Abstract]
    
    Let p be an odd prime and n a natural number. We determine the irreducible constituents of the permutation module induced by the action of the symmetric group S_n on the cosets of a Sylow p-subgroup P_n . In the course of this work, we also prove a symmetric group analogue of a well-known result of Navarro for p-solvable groups on a conjugacy action of N_G(P ). Before describing some consequences of these results, we will give an overview of the background and recent related results in the area.
    
    

• Mittwoch(!), 21. November 2018, 17:15-18:15: Theodosios Douvropoulos [Institut de Recherche en Informatique Fontamentale]
  • Titel: Coxeter numbers: From fake degree palindromicity to the enumeration of reflection factorizations of regular elements [Abstract]
    
    A famous theorem of Cayley states that there are n^{n-2} vertex-labeled trees on n vertices. A different interpretation of this number, due to Hurwitz, is that it counts smallest length factorizations of the Coxeter element (12...n) of S_n in transpositions. As with many fascinating theorems for the Symmetric group, this statement is the shadow of a result that holds for all reflection groups. Bessis has shown after case-by-case calculations that: The number of smallest length reflection factorizations of a Coxeter element c of W is equal to h^n*n!/|W|, where h is the order of the Coxeter element and n the rank of W. We will present in this talk a uniform argument for this statement (that however relies on the BMR-freeness theorem) and partial generalizations of it that hold for arbitrary regular elements and arbitrary length factorizations. A classical approach due to Frobenius translates the above problem into a series of character evaluations. In the absence of a uniform construction of the characters $\chi$ of complex reflection groups, our method first groups the characters together with respect to an invariant called the Coxeter number $c_{\chi}$. It proceeds by making use of a Galois action on the corresponding Hecke algebra characters which was first considered by Malle to prove a palindromicity phenomenon on the fake degrees of W.
    
    

• Donnerstag, 29. November 2018: Lleonard Rubio y Degrassi [University of Leicester]
  
  • Titel: On the Lie structure of $HH^1$ of tame blocks [Abstract]
    
    Blocks are usually classified by Morita or derived equivalence or by stable equivalence of Morita type. Stable equivalences of Morita type are the most general and frequent in modular representation theory but also the least understood. The main reason is that we do not know if many of the invariants for Morita and derived equivalences are still invariants for stable equivalences of Morita type.
    In this context, Hochschild cohomology records crucial information about a block $B$: its first degree component, denoted by $HH^1(B)$ is a Lie algebra and it is invariant under stable equivalences of Morita type. However, there are very few families of blocks for which the Lie algebra structure of $HH^1$ has been calculated. Therefore it is essential to extend these calculations to further families of examples.
    In this talk I will show that if $B$ is a block with tame representation type, then $HH^1(B)$ is a solvable Lie algebra. This is joint work with Sibylle Schroll and Andrea Solotar.
    
    

• Donnerstag, 6. Dezember 2018: Kein Seminar (Nikolaus Conference)

• Donnerstag, 13. Dezember 2018: Ruwen Hollenbach [TU Kaiserslautern]
  • Titel: Quasi-Isolated Blocks of Finite Groups of Lie Type [Abstract]
    
    In a recent paper G. Malle and G. Robinson proposed a modular analogue to the k(B)-conjecture. If B is a p-block with defect group D, then they conjecture that l(B) \leq p^r, where r is the sectional p-rank of D. I will talk about recent progress on this conjecture for finite groups of Lie type.
    
    

• Dienstag(!), 18. Dezember 2018, 17:15-18:15 (Raum: 48-208): Jesua Chavez [Institut de Mathématiques de Jussieu-Paris Rive Gauche]
  • Titel: Howe correspondence between Harish-Chandra series [Abstract]

• Donnerstag, 3. Januar 2019: kein Seminar

• Donnerstag, 10. Januar 2019: Lucas Ruhstorfer [Wuppertal]
  • Titel: Fake Galois Actions [Abstract]

• Donnerstag, 17. Januar 2019: David Stewart [Newcastle]
  • Titel: Gröbner bases, smooth centralisers and the Lefschetz principle  [Abstract]
    
    (Joint with Ben Martin and Lewis Topley). In a paper in the now defunct LMS Journal of Computation I used GAP to compute the Lie-theoretic centralisers in the exceptional groups of elements in their minimal modules in all characteristics, establishing when the centralisers in the groups were smooth. Non-smoothness was only found in very small characteristics, even where there are infinitely many orbits. This led to a question on when all centralisers of elements in a Z-defined representation would be smooth if the characteristic were large enough. With my co-authors we managed to prove this using the Lefschetz principle from model theory applied to Gröbner bases, which gave rise to what we call ‘d-bounded Hopf quadruples’. I’ll explain some of this.
    
    

• Donnerstag, 24. Januar 2019:  Tung Le [University of Pretoria]
  • Titel: On Characters of a Sylow p-subgroup of a Chevalley group G(p^f) [Abstract]

• Donnerstag, 31. Januar 2019: Simon Goodwin [University of Birmingham]
  • Titel: Representations of reduced enveloping algebras for gl_n and restricted Yangians [Abstract]

• Donnerstag, 7. Februar 2019: kein Seminar

• Donnerstag, 14. Februar 2019, 17:00 Uhr(!): Arezoo Aslizadeh [TU Kaiserslautern/ Shahid Beheshti University, Tehran]
  • Titel: The nilpotent multipliers of the direct sum of Lie algebras [Abstract]

Organisatoren: Dr. Niamh Farrell and Dr. Alessandro Paolini

• Donnerstag, 12. April 2018: Kein Seminar.

• Donnerstag, 19. April 2018: Kein Seminar.

• Donnerstag, 26. April 2018: Kein Seminar.

• Donnerstag, 3. Mai 2018: Keivan Mallahi-Karai [Jacobs University, Bremen]
  • Titel: Kirillov's orbit method and the polynomiality of the essential dimension of p-groups

• Montag, 7. Mai 2018: Thomas Gobet [University of Sydney]
  • Titel: Dual and classical generators of Artin groups of spherical type

• Donnerstag, 17. Mai 2018: Zhicheng Feng [TU Kaiserslautern]
  • Titel: On the inductive blockwise Alperin weight condition for special linear and unitary groups

• Donnerstag, 24. Mai 2018: Keine Seminar

• Donnerstag, 31. Mai 2018: Kein Seminar (Fronleichnam)

• Donnerstag, 7. Juni 2018: two seminars.
  • 16.30-17.30: İpek Tuvay [Mimar Sinan Fine Arts University, Istanbul]
    • Titel: Brauer indecomposability of Scott modules for the quadratic group Qd(p)
  • 17.30-18.30: Kivanc Ersoy [Freie Universität Berlin]
    • Titel: Groups with certain conditions on fixed points of automorphisms

• Donnerstag, 14. Juni 2018: Iulian Simion [Babes-Bolyai University, Cluj]
  • Titel: Minimal realizations of finite groups of isometries

• Donnerstag, 21. Juni 2018: Alex Malcolm [Heilbronn Institute for Mathematics, Bristol]
  • Titel: Strong reality in finite simple groups: on products of classes and characters

• Donnerstag, 28. Juni 2018: Kein Seminar

• Donnerstag, 05. Juli 2018: Kein Seminar

• Donnerstag, 12. Juli 2018: Madeleine Whybrow [TU Kaiserslautern]
  • Titel: Constructing Majorana representations

Organisatoren: Jun.-Prof. Dr. Caroline Lassueur and Dr. Alessandro Paolini

• Donnerstag, 26. Oktober 2017: Andrew Mathas [University of Sydney]
  • Titel: Jantzen filtrations and graded Specht modules  
    

    The Jantzen sum formula is a classical result in the representation theory of the symmetric and general linear groups that describes a natural filtration of the Specht modules over any field. Analogues of this result exist for many algebras including the cyclotomic Hecke algebras of type A. Quite remarkably, the cyclotomic Hecke algebras of type A are now know to admit a Z-grading because they are isomorphic to cyclotomic KLR algebras. I will explain how to give an easy proof, and stronger formulation, of Jantzen sum formula for the cyclotomic Hecke algebras of type A using the KLR grading. I will discuss some consequences and applications of this approach.      

• Donnerstag, 02. November 2017: Caroline Lassueur [TU Kaiserslautern]
  
  • Titel: Lifting Morita equivalences with an endo-permutation source

• Donnerstag, 09. November 2017: Kein Seminar

• Donnerstag, 16. November 2017: Olivier Dudas [Université Paris Diderot - Paris 7]
  • Titel: On the unitriangular shape of decomposition matrices for finite reductive groups

• Donnerstag, 23. November 2017: Reda Chaneb [Université Paris Diderot - Paris 7]
  • Titel: Basic sets for unipotent blocks of finite reductive groups

• Donnerstag, 7. December 2017,  Oberseminar Representation Theory : Emil Rotilio [TU Kaiserslautern]
  • Titel: Lie superalgebras in Physics  

    The current understanding of nature finds in the „Standard Model“ the most complete and verified theory (for now). The mathematics it involves heavily relies on Lie theory (Lie groups and Lie algebras). To better describe the universe, phisicists have come up with a „Supersymmetry“ theory (among others). This theory is described in terms of Lie superalgebras. The goal of this talk is to give an overview of which Lie algebras/superalgebras are used in Physics and why they help describing nature.
                    

• Donnerstag, 14. December 2017: Stefano Sannella [University of Birmingham]       
  • Titel: Broué's conjecture and perverse equivalences                  

    The representation theory of a finite group G over a field F of positive characteristic carries many questions that have not been answered yet. Most of them can be stated as global/local conjectures: in various forms, they state that the representation theory of G is somehow controlled by its p-local subgroups. Here we will mostly focus on one of these conjectures, Broué's Abelian Defect Group Conjecture, which might be considered as an attempt to give a structural explanation of what is actually connecting G and its local p-subgroups in the abelian defect case. In particular, we explain how the strategy of looking for a perverse equivalence (a specific type of derived equivalence) works successfully in some cases and how this procedure is related to some Deligne-Lusztig varieties.
                    

• Donnerstag, 21. December 2017: Patrick Wegener [TU Kaiserslautern]
  • Titel: Hurwitz action in elliptic Weyl groups and coherent sheaves on a weighted projective line                  

    Since 2000 the poset of noncrossing partitions attached to a Coxeter
    group (independently introduced by Bessis and Brady-Watt) has gained a
    lot of attention from different areas of mathematics. In 2010 Igusa,
    Schiffler and Thomas showed that there exists an order preserving
    bijection between this poset and the set of thick subcategories in the
    derived category of mod(A) generated by an exceptional sequence, where
    A is a hereditary Artin algebra. Following Happel's classification of
    hereditary categories, it seems natural to ask if there is an analogous
    statement when replacing mod(A) by the category of coherent sheaves on a
    weighted projective line. I will give a short summary on hereditary
    categories, explain how elliptic Weyl groups show up in this context and
    then generalize the result of Igusa-Schiffler-Thomas to tubular weighted
    projective lines. (This is joint work with B. Baumeister and S. Yahiatene.)

• Donnerstag, 11. Januar 2018: Kein Seminar.

• Donnerstag, 18. Januar 2018: Florian Eisele [City, University of London]
  • Titel: A counterexample to the first Zassenhaus conjecture                  

    There are many interesting problems surrounding the unit group U(RG) of the ring RG,
    where R is a commutative ring and G is a finite group. Of particular interest are the finite subgroups of
    U(RG). In the seventies, Zassenhaus conjectured that any u in U(ZG) is conjugate,  in the group U(QG),
    to an element of the form +/-g, where g is an element of the group G. This came to be known as the "Zassenhaus conjecture".
    
    In recent joint work with L. Margolis, we were able to construct a
    counterexample to this conjecture. In this talk I will give an introduction to the various conjectures surrounding finite subgroups of U(RG),
    and how they can be reinterpreted as questions on the (non-)existence of certain R(GxH)-modules, where H is another finite group.
    This establishes a link with the representation theory of finite groups, and I will explain how, p-locally, our example is made up of certain p-permutation modules.   

• Donnerstag, 25. Januar 2018: Petra Schwer [Karlsruher Institut für Technologie] 
  • Titel: Reflection length in affine Coxeter groups                
    

    Affine Coxeter groups have a natural presentation as reflection groups on some
    affine space. Hence  the set R of all its reflections, that is all conjugates of its
    standard generators, is a natural (infinite) set of generators. Computing the reflection
    length of an element in an affine Coxeter group means that one wants to determine
    the length of a minimal presentation of this element with respect to R.
    In joint work with Joel Brewster Lewis, Jon McCammond and T. Kyle Petersen we were
    able to provide a simple formula that computes the reflection length of any element
    in any affine Coxeter group. In this talk I would like to explain this formula, give
    its simple uniform proof and allude to the geometric intuition behind it.  

• Donnerstag, 1. Februar 2018: Kein Seminar

• Donnerstag, 8. Februar 2018: Kein Seminar

Organisator: Dr. Alessandro Paolini

• Donnerstag, 20. April 2017: Kein Seminar
  

• Donnerstag, 27. April 2017: Kivanç Ersoy [TU Kaiserslautern]
  • Titel: Locally finite groups with small centralizers

• Donnerstag, 4. Mai 2017: Emily Norton [Max Planck Institute Bonn]
  • Titel: The \mathfrak{sl}_\infty-crystal combinatorics of higher level Fock spaces

• Donnerstag, 11. Mai 2017: Andreas Bächle [Vrije Universiteit Brussel]
  • Titel: Rationality of groups and centers of integral group rings

• Donnerstag, 18. Mai 2017: Kein Seminar

• Donnerstag, 25. Mai 2017: Kein Seminar

• Donnerstag, 1. Juni 2017: Kein Seminar                          

• Donnerstag, 08. Juni 2017: William Wong [TU Kaiserslautern]
  • Titel: A phenomenon in the representation of SL(2,q) in defining characteristics             

• Donnerstag, 13. Juni 2017: Wolfgang Willems [Otto-von-Guericke-Universität Magdeburg]
  • Titel: On quasi-projective Brauer characters

• Donnerstag, 22. Juni 2017: Baptiste Rognerud [IRMA, Straßburg]
  • Titel: A Morita theory for permutation modules                 

• Donnerstag, 29. Juni 2017: Julian Külshammer [Universität Stuttgart]
  • Titel: Ringel duality as a special case of Koszul duality                
    

• Donnerstag, 05. Juli 2017: Tung Le [University of Pretoria]
  • Titel: On the automorphisms of designs constructed from finite simple groups

• Donnerstag, 13. Juli 2017: Kein Seminar ("Representation Theory in Kaiserslautern" Konferenz)

• Donnerstag, 20. Juli 2017: Yujiao Sun [Universität Stuttgart]
  • Titel: Supercharacter theories for Sylow p-subgroups of finite exceptional groups of Lie type

• *Freitag, 25. August 2017, 14:00-15:00*: Shigeo Koshitani [University of Chiba]
  • Titel: Brauer indecomposability of Alperin-Scott modules for finite non-abelian 2-groups

Organisatoren: Dr. Julian Brough und Jun.-Prof. Dr. Caroline Lassueur

• Donnerstag, 3. November 2016, : Yanjun Liu [TU Kaiserslautern]
  • Titel: Principal and defect-zero blocks of finite groups

• Donnerstag, 24. November 2016, : Niamh Farrell [TU Kaiserslautern/City, University of London]
  • Titel: The rationality of blocks of quasi-simple finite groups

• Donnerstag, 25. November 2016: Jesper Grodal [Københavns Universitet]
  • Titel: Endotrivial modules via homotopy theory

• Donnerstag, 1. Dezember 2016: Emilio Pierro [Universität Bielefeld]
  • Titel: Quantities associated to the subgroup lattice

• Donnerstag, 8. Dezember 2016: Kein Seminar: 9.-10. Dez. Nikolauskonferenz

• Donnerstag, 15. Dezember 2016: Kein Seminar: Konferenz "Finite simple groups, their fusion systems and representations", EPFL

• Donnerstag, 12. Januar 2017: Kein Seminar: 12.-14. Jan. Permutation Konferenz, Bielefeld University   

• Donnerstag, 19. Januar 2017: Iris Köster [Universität Stuttgart]
  • Titel: Sylow Numbers in Character Tables and Integral Group Rings             

• Donnerstag, 26. Januar 2017: Kein Seminar: 27.-28. Jan. Darstellungstheorietage 2016

• Donnerstag, 6. Februar 2017: Magdalena Boos [RUHR- Universtität Bochum]
  • Titel: Using quiver representations to prove finiteness criteria                 

• Donnerstag, 9. Februar 2017: Charles Eaton [University of Manchester]
  • Titel: Loewy lengths of blocks                

• Donnerstag, 8. März 2017: Micheal Geline [Northern Illinois University]
  • Titel: Some quantitative and qualitative aspects of Knörr lattices

Organisatoren: Dr. Thomas Gobet und Dr. Caroline Lassueur

• Donnerstag, 21. April 2016, 15:30-16:30, Raum 48-582: Paul Balmer (UCLA, Bielefeld)
  • Titel: A quick tour of tensor triangular geometry

• Donnerstag, 28. April 2016, 17:00-18:00: Jitendra Bajpai (MPI Bonn) - canceled
  • Titel: Introduction to the theory of hypergeometric groups

• Donnerstag, 5. Mai 2016: no talk (Christi Himmelfahrt)

• Mittwoch, 11. Mai 2016, 17:00-18:00, Raum 48-436: Jay Taylor (Padova)
  • Titel: Sums of Skew Characters of Symmetric Groups

• Donnerstag, 12. May 2016, 17:00-18:00, Raum 48-436: Christopher Voll (Bielefeld)
  • Title: Representation growth of finitely generated nilpotent groups

• Donnerstag, 19. Juni 2016: no talk because of workshop "Branching problems for reductive groups" at IML

• Donnerstag, 26. Juni 2016: no talk because of Fronleichnam   

• Donnerstag, 2. Juni 2016, 17:00-18:00, Raum 48-436: René Reichenbach (Jena)
  • Title: The Broué-Puig *-construction and some applications to 2-blocks            

• Donnerstag, 26. Januar 2017: Kein Seminar: 27.-28. Jan. Darstellungstheorietage 2016

• Donnerstag, 6. Februar 2017: Magdalena Boos [RUHR- Universtität Bochum]
  • Titel: Using quiver representations to prove finiteness criteria                 

• Donnerstag, 9. Februar 2017: Charles Eaton [University of Manchester]
  • Titel: Loewy lengths of blocks                

• Donnerstag, 8. März 2017: Micheal Geline [Northern Illinois University]
  • Titel: Some quantitative and qualitative aspects of Knörr lattices

Organisatoren: Dr. Thomas Gobet und Dr. Caroline Lassueur

• Donnerstag, 15. Oktober 2015, 16:00-17:00, Raum 48-436: Mikaël Cavallin [EPFL, Ecublens, CH]
  • Titel: Restriction of irreducibles and structure of Weyl modules

• Donnerstag, 29. Oktober 2015: Philipp Perepelitsky [TU Kaiserslautern]
  • Titel: p-permutation equivalences between blocks of finite groups

• Donnerstag, 5. November 2015: Benjamin Sambale [TU Kaiserslautern]
  • Titel: Broué's Conjecture for sporadic groups

• Donnerstag, 12. November 2015: Neil Saunders [EPFL, Ecublens, CH]
  • Titel: Irreducible Components of Springer Fibres

• Donnerstag, 19. November 2015: Thomas Gobet [TU Kaiserslautern]
  • Titel: On twisted filtrations on Soergel bimodules and linear Rouquier complexes

• Mittwoch, 25. November 2015: Olivier Dudas [University Paris Diderot - Paris 7, FR]
  • Titel: On the unitriangular shape of decomposition matrices for finite reductive groups

• Donnerstag, 26. November 2015: Chris Bowman [City University, London, UK]
  • Titel: The co-Pieri rule for Kronecker coefficients

• Donnerstag, 3. Dezember 2015: Benedetta Lancellotti [Università degli Studi di Milano-Bicocca, IT]
  • Titel: Trivial source lattices and a strong form of McKay conjecture

• Mittwoch, 9. Dezember 2015, 16:00-17:00, Raum 48-582: Patrick Wegener [Universität Bielefeld]
  • Titel: Hurwitz action in Coxeter Groups

• Donnerstag, 17. Dezember 2015: Oberseminar Complex Reflection Groups

• Donnerstag, 14. Januar 2016: Alessandro Paolini [University of Birmingham, UK]
  • Titel: A reduction of characters of Sylow p-subgroups of finite groups of Lie type

• Donnerstag, 28. Januar 2016: Oliver Goodbourn [Ruhr-Universität Bochum]
  • Titel: Reductive pairs from representations of algebraic groups

• Donnerstag, 4. Februar 2016: Julian Brough [TU Kaiserslautern]
  • Titel: Determining finite group structure from the size of the conjugacy classes

• Donnerstag, 11. Februar 2016: John Murray [Maynooth University, IR]
  • Titel: Strong and weak reality and principal indecomposable modules in characteristic 2

Organisatorinnen: Dr. habil. Britta Späth und Dr. Caroline Lassueur

• Donnerstag, 23. April, 15:30-16:30, Raum 48-582: Ulrike Faltings [TU Kaiserslautern]
  
  • Titel: On the decomposition numbers of F_4(q) for q even
    

• Donnerstag, 30. April, 15:30-16:30, Raum 48-582: Carolina Vallejo [Universitat de València]
  • Titel: Coprime action and Brauer characters

• Dienstag, 12. Mai, 15:30-16:30, Raum 48-436: Danny Neftin [University of Michigan, Ann Arbor]
  • Titel: Monodromy groups of rational functions

• Donnerstag, 21. Mai, 15:30-16:30, Raum 48-519: Vivien Ripoll [Universität Wien]
  • Titel: Coxeter elements in well-generated complex reflection groups

• Donnerstag, 4. Juni: Kein Seminar (Fronleichnam)

• Donnerstag, 15:30-16-30, 11. Juni: Amanda Schaeffer Fry [Metropolitan State University Denver]
  • Titel: Finite groups with an irreducible character of large degree

• Donnerstag, 18. Juni, 17:00-18:00, Raum 48-436: Thomas Gerber [RWTH Aachen]
  • Titel: Weak Harish-Chandra theory for finite unitary groups

• Donnerstag, 25. Juni, 15:30-16:15: Matthias Klupsch [RWTH Aachen]
  • Titel: Supercuspidal modules of finite reductive groups

• Donnerstag, 16. Juli, 17:00-18:00, Seminarraum 48-436: Oksana Yakimova [Friedrich-Schiller-Universität Jena]
  • Titel: On symmetric invariants of semi-direct products

• Donnerstag, 23. Juli: Kein Seminar

Organisatorinnen: Dr. habil. Britta Späth und Dr. Caroline Lassueur

• Donnerstag, 2. Oktober: Shigeo Koshitani [University of Chiba]
  • Titel: Remarks on the Loewy length of a block algebra

• Donnerstag, 30. Oktober: Attila Maróti [TU Kaiserslautern]
  • Titel: Groups equal to a product of three conjugate proper subgroups

• Donnerstag, 6. November: Kein Seminar
  • November 7.-8.: Darstellungstheorie-Tage 2014

• Donnerstag, 27. November: Imke Toborg [Universität Koblenz-Landau]
  • Titel: Local methods need some representation theory to prove Z_3^* results

• Donnerstag, 4. Dezember: Kein Seminar
  • Dezember 5-6.: Nikolauskonferenz Aachen

• Donnerstag, 18. Dezember: Sebastian Herpel [Ruhr-Universität Bochum]
  • Titel: Maximal subalgebras of Cartan Type in the exceptional Lie algebras

• Donnerstag, 8. Januar: Tommy Hofmann [TU Kaiserslautern]
  • Titel: Integrality of Representations of Finite Groups

• Donnerstag, 5. Februar, 17:00 Raum 48-436: Eirini Chavli [Université Paris Diderot - Paris 7]
  • Titel: The BMR freeness conjecture: the exceptional groups of rank 2         

• Donnerstag, 19. Februar, 17:00 Raum 48-436: Barbara Baumeister [Universität Bielefeld]
  • Titel: Moufang twin buildings and Kac-Moody groups

Organisatoren: Britta Späth und Jay Taylor

• 24.04.2014, 17:00-18:00 (Room 48-436): Simon Schmider
  
  • Titel: On Auslander-Reiten components for Hecke algebras of type A
    

• 08.05.2014, 17:00-18:00 (Room 48-436): Frank Himstedt [TU München]
  • Titel: On the decomposition numbers of the groups $\rm SO_7(q)$ and
    $\rm Sp_6(q)$

• 22.05.2014, 17:00-18:00 (Room 48-436): Erwan Biland [Sherbrooke University, Kanada]
  • Titel: Stable equivalences related to the Z*p-theorem

• 28.05.2014, 17:00-18:00 (Room 48-436): Pablo Luka
  
  • Titel: Vertex-bounded defects
    

• 05.06.2014, 15:45-16:45 (Room 48-582): Eugenio Gianelli [Royal Holloway University of London]
  
  • Titel: On permutation modules and decomposition numbers of the symmetric group

• 05.06.2014, 17:00-18:00 (Room 48-436): Hung P. Tong-Viet [Universität Bielefeld]
  
  • Titel: Some results on Brauer character degrees of finite groups
    

• 12.06.2014, 17:00-18:00 (Room 48-436): Martino Garonzi [Università di Padova]
  • Titel: Factorizing a group with conjugate subgroups
    

• 03.07.2014, 16:00-17:00 (Room 48-582): Giovanna Carnovale [Università di Padova]
  • Titel: Conjugacy classes in finite simple groups and pointed Hopf algebras        

• 17.07.2014, 17:00-18:00 (Room 48-436): Martina Lanini [FAU Erlangen-Nürnberg]
  • Titel: Finite dimensional representations of rational Cherednik algebras
    

Organisatorin: Britta Späth

• 07.11.2013, 15:30-16:030 (Room 48-436): Philipp Perepelitsky
  
  • Titel: $p$-permutation equivalences between blocks of finite groups
    

• 14.11.2013, 15:30-16:30 (Room 48-436): Iulian Simion
  • Titel: Refining the Bruhat decomposition
    

• 21.11.2013: no talk
  
  • Baer Kolloqium (23.11.2013)
    

• 28.11.2013, 15:30-16:30 (Room 48-436): Fuat Erdem
  
  • Titel: On the generating graph of a finite group
    

• 05.12.2013: no talk
  
  • Titel: Darstellungstheorietage und Nikolauskonferenz
    

• 12.12.2013, 16:00-17:00 (Room 48-436): Jürgen Müller
  
  • Titel: The Abelian Defect Group Conjecture for sporadic simple groups
    

• 19.12.2013, 15:30-16:30 (Room 48-436): Olivier Dudas
  
  • Titel: Ordering conjugacy classes in Weyl groups
    

• 09.01.2014, 15:30-16:30 (Room 48-436): Caroline Lassueur
  
  • Titel: The position of endo-$p$-permutation modules and relatives in the Auslander-Reiten quiver        

• 16.01.2014, 17:00-18:00 (Room 48-436): Serge Bouc
  
  • Titel: The poset of posets

• 23.01.2014, 15:30-16:30 (Room 48-436): Elisabeth Schulte
  
  • Titel: Alperin's Weight Conjecture - On Inductive Conditions for $G_2(q)$

• 30.01.2014, 15:30-16:30 (Room 48-436): Burkhard Külshammer
  • Titel: Some questions in block theory

• 10.02.2014, 15:30-16:30 (Room 48-436): Alessandro Paolini [University of Birmingham]
  • Titel: A Basis of the Gelfand-Graev Algebra of a Chevalley Group

• 06.03.2014, 10:30-11:30 (Room 48-436): Michel Enguehard [Institut de Mathematique de Jussiue]
  • Titel: Towards a Jordan decomposition of blocks of finite reductive groups