Algebra Seminar
The Algebra Seminar provides graduate students, advanced undergraduate students, and faculty a forum to discuss and/or present Research, Problems, Applications, or Exposition in Algebra. For more information contact Arturo Magidin.
Spring 2022
For the Spring 2022 semester we will usually meet 2:15  3:15 on Fridays. Some meetings will be on Zoom and others will be inperson in Maxim Doucet 208. We may need to change the time and date on occasion to accomodate visitors.
For more information or connection details contact contact Arturo Magidin.

28 January 2022 (postponed from 21 Jan)
More on the BensonSolomon fusion systems
Justin Lynd
UL Lafayette
Abstract: In this seminar Dr. Lynd will expand on his colloquium presentation of Thursday (20 January 2022).
A fusion system can be thought of as a "finite group at a prime p". After some historical remarks around the Classification of the Finite Simple Groups, I will explain what a pfusion system is. Most of the examples of fusion systems we know of come from finite groups, but there do exist many exotic examples, chiefly at odd primes. In fact, we know of just one infinite family of simple exotic fusion systems at the prime 2, the BensonSolomon fusion systems. In the second part of the talk, I will explain some coincidences that allow the BensonSolomon systems to exist and, time permitting, discuss some of what is known about them.
Fall 2021
During the Fall 2021 semester we will meet on Fridays from 1:002:00 in Maxim Doucet Hall, room 208. You can also join us via Zoom! Contact contact Justin Lynd for the Zoom info.

17 September 2021
An introduction to partial groups
Justin Lynd, UL Lafayette
Abstract: A partial group is a set together with a multivariable product which is only defined on a specified set of words in the underlying set. (A group is a partial group in which all products of words are defined.) This notion was introduced by Chermak in 2013 as the basic object in a framework for studying the $p$local structure of a finite group G, i.e. how G conjugates its psubgroups. I will explain briefly some of the history behind Chermak's work, which originates in topology. But mainly I plan give an introduction to partial groups, and explain several examples. This includes the motivational examples, the localities of finite groups. 
24 September 2021
Generalizing the ChermakDelgado lattice of a finite group: a very preliminary report
Arturo Magidin, UL Lafayette
Abstract: In 1989, Andrew Chermak and Alberto Delgado introduced a family of measures for subgroups of a finite group, connecting a subgroup with its centralizer. They then used the measure to obtain interesting results guaranteeing the existence of a characteristic abelian groups of bounded index.
The normalized version of the measure leads to a collection of subgroups which form an interesting selfdual sublattice of the lattice of all subgroups, called the ChermakDelgado lattice of the finite group.
In joint work with William Cocke, LC Kappe, and Elizabeth Wilcox, we are looking at possible generalizations of the measure that connects subgroups with certain "relative marginal subgroups." I will discuss what we are trying to do, what the obstacles are, and what questions these obstacles suggest we (and others) may want to address. 
1 October 2021
Exotic and blockexotic fusion systems
Patrick Serwene, Technische Universität Dresden (TU Dresden)
Abstract: One of the main problems in the theory of fusion systems is the question whether a fusion system arises in the form of a finite group if and only if it arises in the form of a pblock of a finite group. There is a conjecture saying that a fusion system is induced by a group if and only if it is induced by a block. We present reduction theorems for this problem reducing it to blocks of quasisimple groups in certain cases. One of these reductions settles the conjecture for the family of Parker–Semeraro fusion systems. We discuss ongoing work concerning our strategy to prove the conjecture for some groups of Lie type. 
29 October 2021
Endotrivial modules for cyclic pgroups and generalized quaternion groups via Galois descent
Richard Wong, UCLA
Abstract: One problem of interest in modular representation theory of finite groups is in computing the group of endotrivial modules. This group was originally computed by CarlsonThevenaz using the theory of support varieties. However, one can approach this problem through homotopy theory, where this group is known as the Picard group of the stable module category. Jointly with Jeroen van der Meer, we provide new, homotopical proofs of their results for the quaternion group of order 8, generalized quaternion groups, and cyclic pgroups using descent methods. 
5 November 2021
Decreasing paths of triangles
Leonel Robert, UL Lafayette
Abstract: I will discuss a geometric problem on decreasing paths of triangles, as well as its higher dimensional generalizations (to tetrahedra, etc). The problem can be reformulated in terms of nonhomogeneous Markov chains. In this context it is known as the "embedding problem". The problem can be approached using methods from control theory, but the farthest reaching results so far rely only on elementary methods from algebra and geometry. 
12 November 2021
Two problems related to tilting modules for algebraic groups
Paul Sobaje, Georgia Southern University
Abstract: The modular representation theory of reductive algebraic groups (general linear groups being an example of such groups) has a number of longstanding open problems. Several of these problems have conjectured resolutions that involve special modules known as indecomposable tilting modules. In this talk we will look at how tilting modules relate to two problems in particular: 1) integrating representations from the Lie algebra to the algebraic group, and 2) finding a character formula for the irreducible representations. A good deal of background material will be provided throughout. 
19 November 2021
Asymptotic Behavior of Tensor Powers of Modular Representations and Banach Algebras
Peter Symonds, University of Manchester
Abstract: Let M be a finite dimensional modular representation of a finite group G. We consider the dimension of the nonprojective part of a tensor power of M, and how this grows as the power increases. From this we obtain an invariant of M, which we investigate using tools from representation theory and from the theory of commutative Banach algebras. (Joint work with Dave Benson.)
Spring 2020

11 February 2020
The ChermakDelgado Lattice and generalizations I: An introduction
Arturo Magidin (UL Lafayette)
In 1989, Andrew Chermak and Alberto Delgado introduced a "measure" for subgroups of a group $G$ being acted on by a group $H$: given a subgroup $A\leq G$, $m_r(A) = A^rC_H(A)$. The set of subgroups for which the measure achieves its largest value has interesting properties: for example, it forms a sublattice of the lattice of subgroups of $G$, is selfdual, and all its elements are equal to their double centralizers.
LC Kappe, Elizabeth Wilcox, William Cocke and are currently exploring some generalizations, replacing the centralizer with some other constructions. As a leadup to discussing some of those results, I will discuss the properties of the measure and some of the results about the lattice. 
18 February 2020
The ChermakDelgado Lattice and generalizations II: A digression into words and margins
Arturo Magidin (UL Lafayette)
The center of a group and the commutator subgroup play roles that are "dual" to each other in a way that was formalized by Philip Hall in the 1940s, as part of a proposed scheme to classify finite $p$groups. He also indicated how these notions could be generalized to other subgroups, including but not restricted to terms of the upper and lower central series. These are the marginal and verbal subgroups; the latter were well known at the time, but the former and the connection between them was new.
One can view centralizer subgroups as a kind of "relative center"; the point of departure for our attempts at generalizing the ChermakDelgado construction lattice is trying to take this view and apply it to the general setting of marginal and verbal subgroups, by defining a "relative marginal subgroup".
To put this in context, I will give an introduction to verbal and marginal subgroups. 
3 March 2020
The ChermakDelgado Lattice and generalizations III
Arturo Magidin (UL Lafayette) 
17 March 2020 (CANCELLED)
Lower Finite Modules over Commutative Rings
Luke Harmon (University of Colorado Colorado Springs)
Abstract: A partially ordered set (P,lt) is lower finite provided P is infinite and for each x in P, there are but finitely many elements y in P such that y lt x. We will call a module M lower finite if the set of proper submodules of M, partially ordered by settheoretic containment, is lower finite. We will use the (wellstudied) class of Jonsson modules (along with other classical results) to classify the lower finite modules over a commutative ring with identity.
Fall 2019
During the Fall 2019 semester we will meet on Mondays from 4:005:00 in Maxim Doucet Hall, room 201.

16 September 2019
A Partial Order on Subsets of Baer Bimodules with Applications to C*Modules
Gary Birkenmeier
Abstract: In a series of seminars, the concept of Baer (p, q)sets is introduced. Using this notion, we define Rickart, Baer, quasiBaer and piBaer (S, R)bimodules, respectively. We show how these conditions relate to each other. We also develop new properties of the minus partial order \leq, we extend the relation \leq to (S, R)bimodules, and use it to characterize the aforementioned Rickart, Baer, quasiBaer, and piBaer (S, R)bimodules. Note that \leq generalizes the natural order on the projections of a C*algebra. Moreover we specify subsets K of the power set of a (S, R)bimodule for which \leq is a partial order and for which \leq determines a lattice. We analyze the relation \leq by examining the associated Baer (p, q) sets. Finally, we apply our results to C*modules. Examples are provided to illustrate and delimit our results. 
23 September 2019
Gary Birkenmeier 
30 September 2019
Gary Birkenmeier 
7 October 2019
Gary Birkenmeier 
14 October 2019
Normal subgroups of invertibles and of unitaries in C^*algebras
Leonel Robert Gonzalez
Abstract: I will talk about my work on the normal subgroups of the group of invertibles in the connected component of the identity in a C*algebra. 
4 November 2019
Algebraic properties of modular tensor categories
Yilong Wang
Louisiana State University
Abstract: Modular tensor categories (MTC) are categorical generalizations of finite abelian groups with nondegenerate quadratic forms. They give rise to invariants of links and 3manifolds that has similar "quantum" nature as the Jones polynomial. They also provide representations of SL(2, Z/NZ) and mapping class groups of higher genus surfaces which can be viewed as derived from (2+1)topological quantum field theories (TQFTs) associated to the MTCs. MTCs are also indispensable ingredients in the setup of the mathematical foundations for topological quantum computation.
In this talk, we will introduce the notion of modular tensor categories with an emphsis on its rich connection with representation theory, (2+1)TQFTs and topological quantum computing. Then we will present our recent work on the algebraic properties of MTCs and the TQFTs associated to them. 
11 November 2019
Principal Series Representations of GL(2) Over Finite Fields
Regina Poderzay
UL Lafayette
Abstract: The goal of this talk is to construct the principal series representations of GL(2). To begin, we observe rudimentary results and examples using prerequisite knowledge from linear algebra and group theory. This is followed by inducing new representations from old ones. A key component in the classification of induced representations is Mackey’s theorem. At last is where we construct the principal series representations. This construction is motivated by the Bruhat decomposition of GL(2) into the Borel subgroup and is achieved by counting the conjugacy classes of GL(2,q). 
22 November 2019 (Friday, 3:004:00)
Linearly Presented Toric Edge Ideals of Bipartite Graphs
Jason McCullough
Iowa State University
Abstract: Let G = (V,E) be a finite simple graph and let k be a field. Denote by k[E] the polynomial ring with edges of G identified with variables and k[V] the polynomial ring with vertices of G identified with variables. The toric edge ring of G is the ksubalgebra of k[V] generated by v_i*v_j for all {i,j} in E. If we take the canonical surjection from k[E] to k[G], the kernel defines a (prime) toric ideal called the toric edge ideal I_G of G. In the case when G is a complete bipartite graph K_m,n, I_G is the defining ideal of the Segre embedding of P^(m1) x P^(n1) in P^(mn  1). It is wellknown that generators of I_G correspond to even closed walks in G. Hibi and Herzog previously characterized those bipartite graphs G such that I_G is generated by quadratic polynomials. We present a combinatorial description of those ideals whose ideals are linearly presented. This result has connections to polyomino ideals and Hibi rings that I will explain. This is joint work with Zach Greif.
Spring 2019
During the Spring 2019 semester we will meet on Fridays from 2:103:10 in Maxim Doucet Hall, room 210.

1 February 2019
The structure of a minimal counterexample to the FeitThompson theorem
George Glauberman
University of Chicago
Abstract: This talk supplements my colloquium talk by describing in more detail the proof of the FeitThompson Theorem. 
15 February 2019
Minimal bisets for fusion systems and blocks of finite group algebras, I
Justin Lynd
Abstract: I will discuss the background for ongoing work with M. Gelvin (Bilkent) in which we investigate the question: which finite groups are minimal bisets for their fusion systems? As it turns out, this question is closely related to the following question in the modular representation theory of finite groups: when k is an algebraically closed field of characteristic p, for which finite groups G is the group algebra kG indecomposable as a kalgebra?
A saturated fusion system F over a finite pgroup S is a finite category with objects the subgroups of S and with morphisms between subgroups which are "conjugationlike" group homomorphisms. Here, S plays the role of a Sylow psubgroup of the category. In the first talk, I will give the definition of a saturated fusion system F. Although F need not be the localization of any finite group G, one can define an SS biset associated with F that plays the same role as the SS biset G, whenever F is the localization of G at p. 
8 March 2019
Minimal bisets for fusion systems and blocks of finite group algebras, II
Justin Lynd 
15 March 2019
Minimal bisets for fusion systems and blocks of finite group algebras, III
Justin Lynd 
22 March 2019
Minimal bisets for fusion systems and blocks of finite group algebras, IV
Justin Lynd
Abstract: In the first three talks, we have defined the notion of a saturated fusion system \F on a finite pgroup S, and we have associated to it an SS biset X. When \F is the fusion system of a finite group G on its Sylow psubgroup S, then one may take X = G. But such a characteristic biset is not uniquely determined by \F. In the remaining talks, we will look at the unique up to isomorphism minimal such biset under inclusion, and we will try to bring out the connection between this minimal biset, when \F = \F_S(G), and the blocks of the group algebra kG. 
25 April 2019
Minimal bisets for fusion systems and blocks of finite group algebras, V
Justin Lynd
Abstract: In the first three talks, we have defined the notion of a saturated fusion system \F on a finite pgroup S, and we have associated to it an SS biset X. When \F is the fusion system of a finite group G on its Sylow psubgroup S, then one may take X = G. But such a characteristic biset is not uniquely determined by \F. In the remaining talks, we will look at the unique up to isomorphism minimal such biset under inclusion, and we will try to bring out the connection between this minimal biset, when \F = \F_S(G), and the blocks of the group algebra kG.
Fall 2018
During the Fall 2018 semester we will meet on Fridays from 2:103:00 in Maxim Doucet Hall, room 201.

14 September 2018
Closure operators on subgroup and other lattices
Arturo Magidin
Abstract: I will talk about joint work with Martha Kilpack, in which we determined all finite lattices L for which the lattice of closure opeartors on L is isomorphic to the lattice of subgroups of a group; and also the same problem but starting from the lattice of subgroups of an infinite group. 
21 September 2018
Closure operators on subgroup and other lattices II
Arturo Magidin
Abstract: I will continue the series of talks about joint work with Martha Kilpack, in which we determined all finite lattices L for which the lattice of closure operators on L is isomorphic to the lattice of subgroups of a group; and also the same problem but starting from the lattice of subgroups of an infinite group.
I will present our main "exclusion result", which provides that certain lattices L do not have the desired property, as well as a reduction result that allows us to invoke inductive arguments. If time permits, we will complete the determination of all finite lattices L for which co(L) is isomorphic to sub(G) for some group G. 
28 September 2018
Closure operators on subgroup and other lattices III
Arturo Magidin
Abstract: I will continue the series of talks about joint work with Martha Kilpack, in which we determined all finite lattices L for which the lattice of closure operators on L is isomorphic to the lattice of subgroups of a group; and also the same problem but starting from the lattice of subgroups of an infinite group.
The next step is relate some downsets on the lattice of closure operators co(L) with the closure operators on certain subsets of L; this will allow us to show that if co(sub(G)) is isomorphic to a subgroup lattice, and N is a normal subgroup of G, then co(sub(G/N)) is also a subgroup lattice. This allows for inductive arguments on G, since we have already reduced the problem to groups whose order is of the form p^a*q^b. 
12 October 2018
Closure operators on subgroup and other lattices IV
Arturo Magidin
Abstract: I will finish my series of talks about joint work with Martha Kilpack, in which we determined all finite lattices L for which the lattice of closure operators on L is isomorphic to the lattice of subgroups of a group; and also the same problem but starting from the lattice of subgroups of an infinite group.
To finish off we will consider the case where G is an infinite group, leading to closure operators on an infinite lattice. We will discuss some technical issues that arise from this, and how the notion of "compact element" of a lattice and "algebraic closure operator" come in to cover the breach. Finally, we determine all infinite groups G for which the lattice of algebraic closure operators on Sub(G) form a subgroup lattice. 
19 October 2018
πBaer Rings
Yeliz Kara
Abstract: I will talk about joint work with Gary F. Birkenmeier and Adnan Tercan, in which we introduced and investigated the concept of πBaer rings. I will present connections between the πBaer condition and the related conditions such as the Baer and quasiBaer conditions. 
19 October 2018
πBaer Rings II
Yeliz Kara
Abstract: I will complete the series of talks about joint work with Gary F. Birkenmeier and Adnan Tercan, in which we introduced and investigated the concept of πBaer rings. I will explain the πBaer ring results on polynomial rings and 2by2 generalized upper triangular matrix rings. 
2 November 2018
Update on the Classification of Indecomposable QuasiFrobenius Rings
Gary Birkenmeier
Abstract: This talk will review and update the nilary quasiFrobenius rings. Recall that a ring R with 1 is "nilary" if AB = 0 implies that either A or B is nilpotent, for all ideals A and B of R. A ring is "quasiFrobenius", denoted QF, if it is right selfinjective and right Noetherian. 
9 November 2018
Update on the Classification of Indecomposable QuasiFrobenius Rings II
Gary Birkenmeier
Abstract: This talk will review and update the nilary quasiFrobenius rings. Recall that a ring R with 1 is "nilary" if AB = 0 implies that either A or B is nilpotent, for all ideals A and B of R. A ring is "quasiFrobenius", denoted QF, if it is right selfinjective and right Noetherian. 
30 November 2018
Update on the Classification of Indecomposable QuasiFrobenius Rings II
Gary Birkenmeier
Abstract: This talk will review and update the nilary quasiFrobenius rings. Recall that a ring R with 1 is "nilary" if AB = 0 implies that either A or B is nilpotent, for all ideals A and B of R. A ring is "quasiFrobenius", denoted QF, if it is right selfinjective and right Noetherian.
Spring 2018
During the Spring 2018 semester we will meet on Tuesdays from 4:004:50 in Maxim Doucet Hall room 210.

23 January 2018
A Description of indecomposable QFrings, part 1
Gary Birkenmeier
Abstract: In this series of talks, I will present a classification of indecomposable QFrings in terms of the essentiality of the ideals generated by primitive idempotents. 
23 January 2018 (4:305:30 TIME CHANGE)
A Description of indecomposable QFrings, part 2
Gary Birkenmeier 
13 February 2018
No seminar this week 
20 February 2018
No seminar this week 
27 February 2018
no seminar this week 
6 March 2018
No seminar this week 
13 March 2018
No seminar this week 
27 March 2018
A Description of indecomposable QFrings, part 3
Gary Birkenmeier 
3 April 2018
no seminar this week (Spring Break) 
10 April 2018
A Description of indecomposable QFrings, part 4
Gary Birkenmeier 
17 April 2018
Support Varieties for Algebraic Groups and the Humphreys Conjecture
William Hardesty
Louisiana State University
Abstract: I will begin by introducing the notion of the support variety of a module over a finite group scheme. This will be followed by a brief overview of classical results and calculations for the case when the finite group scheme is the first Frobenius kernel of a reductive algebraic group G. In 1997, J. Humphreys conjectured that the support varieties of indecomposable tilting modules for G (a very important class of modules) is controlled by a combinatorial bijection, due to G. Lusztig, between nilpotent orbits and a certain collection of subsets of the affine Weyl group called "canonical cells". This later became known as the "Humphreys conjecture". I will discuss some recent developments concerning this conjecture, including its complete verification for G = GL(n) (appearing in my thesis) as well as some additional results in other types appearing in joint work with P. Achar and S. Riche. 
9 May 2018 (4:005:00 WEDNESDAY room 209)
An application of algebra to topology
George Glauberman
University of Chicago
Abstract: The theory of fusion systems is a new branch of mathematics with applications to finite group theory and algebraic topology. In particular, it is involved in a result in topology known as the MartinoPriddy Conjecture, which was proved recently by assuming the classification of finite simple groups. New research with J. Lynd has removed the classification from the proof by using group theory. I plan to describe these topics and some open problems.
Fall 2017
During the Fall 2017 semester we will meet on Tuesdays from 4:004:50 in Maxim Doucet Hall room 210.

19 September 2017
Some ideas and methods from the classification of the finite simple groups
Justin Lynd
Abstract: I intend to give a historical and highlevel overview of the original program for the classification of the finite simple groups. Depending on one's point of view, this is a quest that began either in the late 1890s or in 1954, and it ended either in the early 1980s or in 2004. We will begin at the first beginning and end roughly at the first end. In the middle, the focus will be on the ideas behind the program, which partitions the collection of finite simple groups into three classes: the groups of low 2rank (small), the groups of component type (odd), and the groups of characteristic 2type (even). Inasmuch as there will be any details (unlikely, but this depends on one's definition of "details"), we will focus on the identification of groups in the small and odd cases. 
26 September 2017
Some ideas and methods from the classification of the finite simple groups, part 2
Justin Lynd 
10 October 2017
Some ideas and methods from the classification of the finite simple groups, part 3
Justin Lynd 
24 October 2017
Some ideas and methods from the classification of the finite simple groups, part 4
Justin Lynd 
31 October 2017
Some ideas and methods from the classification of the finite simple groups, part 5
Justin Lynd
Spring 2017
During the Spring 2017 semester we will meet on Fridays from noon12:50 in Maxim Doucet Hall room 214.

27 January 2017
When is the lattice of closure operators on a finite lattice isomorphic to a subgroup lattice?
Arturo Magidin
Abstract: (This is joint work with Martha Kilpack of Brigham Young University.)
A lattice is a partially ordered set in which every pair of elements have a least upper bound and a greatest lower bound; it can also be viewed as an algebra with two binary operators satisfying certain identities. A typical example of a lattice is the lattice of all subgroups of a given group, ordered by inclusion (or more generally, of all substructures of a given structure).
A closure operator on a partially ordered set P is a function f mapping P into P such that f satisfies three conditions:
(i) f is increasing: x less than or equal to f(x) for all x in P;
(ii) f is isotone: if x less than or equal to y, then f(x) less than or equal to f(y) for all x,y in P;
(iii) f is idempotent: f(f(x)) = f(x).
We can partially order all closure operators on P, by letting f less than or equal to g if and only if f(x) less than or equal to g(x) for all x in P. If P is a lattice, then this makes the set of all closure operators on P into a lattice.
It is a theorem of Birkhoff that every complete lattice is the lattice of subalgebras of some (possibly infinitary algebra); and a theorem of Whitman that every lattice can be embedded as a sublattice of a subgroup lattice. This leads to the question of which lattices of closure operators are isomorphic to the subgroup lattice of a group.
Previously, we had shown that if we look at the closure operators on a subgroup lattice Sub(G), then this resulting lattice, c.o.(Sub(G)) is itself a subgroup lattice if and only if G is cyclic of prime power order. We will extend the investigation first to the case of closure operators on an arbitrary finite lattice; and later, to the lattice of subgroups of an infinite group. 
3 February 2017
When is the lattice of closure operators on a finite lattice isomorphic to a subgroup lattice? (part 2)
Arturo Magidin 
10 February 2017
When is the lattice of closure operators on a finite lattice isomorphic to a subgroup lattice? (part 3)
Arturo Magidin 
17 February 2017
When is the lattice of closure operators on a finite lattice isomorphic to a subgroup lattice? (part 4)
Arturo Magidin 
24 February 2017
If G is an infinite group, when is the lattice of algebraic closure operators on Sub(G) isomorphic to the subgroup lattice of a group K?
Arturo Magidin 
3 March 2017
When is the lattice of closure operators on a finite lattice isomorphic to a subgroup lattice? (last part)
Arturo Magidin 
10 March 2017 (SPECIAL TIME 12:20)
A description of indecomposable quasiFrobenius rings
Gary Birkenmeier
Abstract In this talk, we characterize a nilary QFring R in terms of the essentiality of the ideals ReR where e is a primitive idempotent of R. Recall that a ring R is nilary if AB = 0 implies either A or B is nilpotent for all ideals A, B of R. Note that nilary rings are indecomposable rings. This is a preliminary report on joint research with Omar A. AlMallah andHafedh M. AlNoghashi. 
24 March 2017
A description of indecomposable quasiFrobenius rings (part 2)
Gary Birkenmeier 
31 March 2017
A description of indecomposable quasiFrobenius rings (part 3)
Gary Birkenmeier 
7 April 2017
A description of indecomposable quasiFrobenius rings (part 4)
Gary Birkenmeier