Date and time: Thursday 5 August 15:30–17:00 AEST
Xuhua He, Chinese University of Hong Kong
Seminar title: Tits groups of Iwahori-Weyl groups and presentations of Hecke algebras
Abstract: Let G(ℂ) be a complex reductive group and W be its Weyl group. In 1966, Tits introduced a certain subgroup of G(ℂ), which is an extension of W by an elementary abelian 2-group. This group is called the Tits group and provides a nice lifting of W.
In this talk, I will discuss a generalization of the notion of the Tits group T to a reductive p-adic group G. Such T, if exists, gives a nice lifting of the Iwahori-Weyl group of G. I will show that the Tits group exists when the reductive group splits over an unramified extension of the p-adic field and will provide an example in the ramified case that such a Tits group does not exist. Finally, as an application, we will provide a nice presentation of the Hecke algebra of the p-adic group G with ln-level structure.
This talk is based on the recent joint work with Ganapathy.
Speaker bio: Xuhua He is the Choh-Ming Professor of Mathematics at the Chinese University of Hong Kong. He works in pure mathematics. His research interests include Arithmetic geometry, Algebraic groups, and representation theory. He received his Bachelor’s degree in mathematics from Peking University in 2001 and a Ph.D. degree from MIT in 2005 under the supervision of George Lusztig. He worked as a member at the Institute for Advanced Study during 2005-2006 and Simons Instructor at Stony Brook University during 2006-2008. He worked at the Hong Kong University of Science and Technology during 2008-2014 as an assistant Professor and associated Professor, and then moved to the University of Maryland during 2014-2019 as a Full Professor of Mathematics before joining CUHK in 2019. He received the Morningside Gold Medal of Mathematics in 2013, the Xplorer Prize in 2020 and is an invited sectional speaker of the International Congress of Mathematicians in 2018.
Registration: Zoom meeting link
Date and time: Tuesday 3, Monday 9 & Monday 16 August 11:00–12:00 AEST
Vladimir Bazhanov, Australian National University
Seminar title: Yang-Baxter maps
Seminar information: Professor Vladimir Bazhanov will give a short course of lectures on Yang-Baxter maps.
The topic lies on the intersection of the theory of quantum groups and discrete integrable equations.
Registration: Zoom meeting link
Date and time: Thursday 19 August 10:05–10:55 AEST
Lauren Williams, Harvard University
Seminar title: Schubert polynomials, the inhomogeneous TASEP, and evil-avoiding permutations
Abstract: The totally asymmetric simple exclusion process (TASEP) was introduced around 1970 as a model for translation in protein synthesis and traffic flow.
It has interesting physical properties (e.g. boundary-induced phase transitions) and also beautiful mathematical properties. The inhomogeneous TASEP is a Markov chain of weighted particles hopping on a ring, in which the probability that two particles interchange depends on the weight of those particles. If each particle has a distinct weight, then we can think of this as a Markov chain on permutations. In many cases, the steady state probabilities can be expressed in terms of Schubert polynomials. Based on joint work with Donghyun Kim.
Speaker bio: Lauren Williams is the Robinson professor of mathematics at Harvard and the Seaver Professor at the Harvard Radcliffe Institute. Her research is in algebraic combinatorics. Williams received her BA in mathematics from Harvard College in 2000, and her PhD from MIT in 2005. Subsequently, she was a postdoc at UC Berkeley and Harvard, then a faculty member at UC Berkeley from 2009 to 2018, before returning to Harvard in 2018. She is the recipient of a Sloan Research Fellowship, an NSF CAREER award, the AWM-Microsoft research prize, and is an Honorary member of the London Mathematical Society.
Registration: Zoom meeting link to come
Date and time: Friday 26 August 15:30–17:00 AEST
Hankyung Ko, Uppsala University
Seminar title: A singular Coxeter presentation
Abstract: A Coxeter system is a presentation of a group by generators and a specific form of relations, namely the braid relations and the reflection relations. The Coxeter presentation leads to, among others, a similar presentation of the (Iwahori-)Hecke algebras and the Kazhdan-Lusztig theory, which provides combinatorial answers to major problems in Lie theoretic representation theory and geometry. Extending such applications to the `singular land’ requires the singular version of the Hecke algebra. Underlying combinatorics of the singular Hecke algebra/category comes from the parabolic double cosets and is the first step in understanding the singular Hecke category. In this talk, I will present a Coxeter theory of the parabolic double cosets developed in a joint work with Ben Elias. In particular, I will explain a generalization of the reduced expressions and describe the braid and non-braid relations.
Registration: Zoom meeting link to come
Date and time: TBA
Bronwyn Hajek, University of South Australia
Seminar title: Analytic solutions for nonlinear problems in biology
Abstract: Classical and nonclassical Lie point symmetry analysis are powerful techniques that can sometimes be used to construct analytic solutions to nonlinear partial differential equations. In this talk, I’ll outline both the classical and nonclassical methods in some detail. I’ll then describe a number of problems from math biology where the nonclassical symmetry technique has yielded useful analytic solutions. In particular, I’ll describe problems involving determining the minimum size for a nature reserve, tumour modelling, calcium fertilisation waves on amphibian eggs, and mammalian fertilisation waves. I’ll also talk briefly about compactly supported analytic solutions.
Bio: Bronwyn’s research interests lie in developing and solving mathematical models using nonlinear partial differential equations. She is motivated by many areas of application, including biological invasions, cell biology, viscous flow, and physical chemistry. She has a particular focus on the use of Lie symmetry techniques to construct analytic solutions of nonlinear reaction-diffusion equations.
Registration: Zoom meeting link
Recordings of most SMRI seminars are available on the SMRI YouTube channel. There are two main streams of seminars:
The following seminar series involving SMRI staff and visitors are not separately listed below:
- Hilbert schemes (September–December 2020). Speakers: Anthony Henderson, Emily Cliff, Joe Baine, Anthony Licata, Joshua Ciappara, Peter McNamara
- Langlands correspondence and Bezrukavnikov’s equivalence (March 2019–July 2020, recordings April–July 2020). Speaker: Geordie Williamson
In addition to the seminars listed below, SMRI staff and visitors have spoken in the Informal Friday Seminars and other seminars of the School of Mathematics and Statistics, which can be viewed on the School’s upcoming Seminars & Conferences page.
Date and time: Friday 23 July
Shrawan Kumar, University of North Carolina
Seminar title: Root components for tensor product of affine Kac-Moody Lie algebra modules
Abstract: This is a joint work with Samuel Jeralds. Let 𝔤 be an affine Kac-Moody Lie algebra and let λ, µ be two dominant integral weights for 𝔤. We prove that under some mild restriction, for any positive root β, V(λ) ⊗ V(µ) contains V(λ + µ – β) as a component, where V(λ) denotes the integrable highest weight (irreducible) 𝔤-module with highest weight λ. This extends the corresponding result by Kumar from the case of finite dimensional semisimple Lie algebras to the affine Kac-Moody Lie algebras. One crucial ingredient in the proof is the action of Virasoro algebra via the Goddard-Kent-Olive construction on the tensor product V(λ) ⊗ V(µ). Then, we prove the corresponding geometric results including the higher cohomology vanishing on the 𝒢-Schubert varieties in the product partial flag variety 𝒢/𝒫 × 𝒢/𝒫 with coefficients in certain sheaves coming from the ideal sheaves of 𝒢-sub Schubert varieties. This allows us to prove the surjectivity of the Gaussian map.
Seminar notes: PDF document
Thursday, 8 July
Ulrich Thiel, University of Kaiserslautern
Seminar title: Towards the classification of symplectic linear quotient singularities admitting a symplectic resolution
Thursday, 24 June 2021
Gus Lonergan, A Priori Investment Management LLC
Seminar title: Geometric Satake over KU
About the speaker: Gus Lonergan is the Chief Mathematician at A Priori Investment Management LLC. He was previously a L.E. Dickson Instructor in the mathematics department at the University of Chicago. He is interested in representation theory.
Lonergan completed his PhD at MIT under Roman Bezrukavnikov; the thesis was an attempt to understand mod p phenomena in algebraic topology in the context of geometric representation theory. He attended Cambridge University for his undergraduate and master’s degree. He plays a little music on the side.
Thursday, 17 June 2021
Magdalena Boos, Ruhr University Bochum
Seminar title: Advertising symmetric quivers and their representations
Abstract: We introduce the notion of a symmetric quiver as provided by Derksen and Weyman in 2002 and discuss symmetric degenerations in this context (which correspond to orbit closure relations in the symmetric representation variety). After motivating our particular interest in the latter by presenting connections to group actions in algebraic Lie Theory, we explain our main questions: are symmetric degenerations induced by “usual” degenerations in the representation variety of the underlying quiver? We look at (counter)examples and recent results. This is joint work with Giovanni Cerulli Irelli.
Thursday, 10 June 2021
Behrouz Taji, University of Sydney
Seminar title: Projective families of varieties through birational geometry and Hodge theory
Abstract: In the 1920s, building on Fermat’s Last Theorem, Mordell conjectured that the set of rational points of any smooth projective curve of genus at least two, over any number field, is finite. In the 1960s, Shafarevich turned this into a purely algebro-geometric conjecture involving families of smooth projective curves. Parshin, Arakelov and Faltings settled this conjecture by showing that the base spaces of such families are in some sense hyperbolic, as long as there is some variation in the algebraic structure of the fibers. Inspired by recent advances in birational geometry, Kebekus and Kovacs conjectured that these hyperbolicity type properties should hold for a vast class of projective families, with fibers of arbitrary dimension. In this talk I will discuss this conjecture and my solution to it. I will also talk about more recent progress in this area, based on a joint work with Kovacs (University of Washington).
Seminar slides: PDF document
Wednesday, 9 June 2021
Paul Zinn-Justin, University of Melbourne
Seminar title: Generic pipe dreams, conormal matrix Schubert varieties and the commuting variety
Thursday, 3 June 2021
Uri Onn, Australian National University
Seminar title: Base change and representation growth of arithmetic groups
Thursday, 20 May 2021
Stephan Tillmann, University of Sydney
Seminar title: On the space of properly convex projective structures
I will outline joint work with Daryl Cooper concerning the space of holonomies of properly convex real projective structures on manifolds whose fundamental group satisfies a few natural properties. This generalises previous work by Benoist for closed manifolds. A key example, computed with Joan Porti, is used to illustrate the main results.
13 May 2021
Reinout Quispel, La Trobe University
Seminar title: How to discover properties of differential equations, and how to preserve those properties under discretization
The first part will be introductory, and will address the question:
Given an ordinary differential equation (ODE) with certain physical/geometric properties (for example a preserved measure, first and/or second integrals), how can one preserve these properties under discretization?
The second part of the talk will cover some more recent work, and address the question:
How can one deduce hard to find properties of an ODE from its discretization?
Bio: Reinout Quispel was an undergraduate at the University of Utrecht (the Netherlands) for nine years, before obtaining a PhD on the discretization of soliton theory from Leiden University in 1983. He moved to Australia for a three-year position in 1986 and is still there 35 years later. His main areas of expertise are in integrable systems and in the geometric numerical integration of differential equations. He was awarded the Onsager Professorship and Medal by the Norwegian University of Science and Technology (NTNU) in 2013.
6 May 2021
Shun-Jen Cheng, Institute of Mathematics, Academia Sinica
Seminar title: Representation theory of exceptional Lie superalgebras
In the second part of the talk we shall discuss the representation theory of these Lie superalgebras and explain the irreducible character problem in the BGG category. Our main focus will be on our computation of the irreducible characters for two of the exceptional Lie superalgebras. This part is based on recent joint works with C.-W. Chen, L. Li, and W. Wang.
22 April 2021
Marcy Robertson, University of Melbourne
Seminar title: Expansions, completions and automorphisms of welded tangled foams
This classification allows us to connect these “welded tangled foams” to the Kashiwara-Vergne conjecture in Lie theory. In work in progress, we show that the group of homotopy automorphisms of the (rational completion of) the wheeled prop of welded foams is isomorphic to the group of symmetries KV, which acts on the solutions to the Kashiwara-Vergne conjecture. Moreover, we explain how this approach illuminates the close relationship between the group KV and the pro-unipotent Grothendieck–Teichmueller group.
Bio: Marcy Robertson obtained her PhD in Algebraic Topology from the University of Illinois at Chicago in 2010. From there she worked in Canada, France and her native United States before settling down in Australia 2015. She is now a Senior Lecturer of Pure Mathematics at the University of Melbourne.
15 April 2021
Yury Stepanyants, University of Southern Queensland
Seminar title: The asymptotic approach to the description of two dimensional soliton patterns in the oceans
The suggested approach is equally applicable to a wide class of non-integrable equations too. As an example, the asymptotic theory is applied to the description of wave patterns in the 2D Benjamin-Ono equation describing internal waves in the infinitely deep ocean containing a relatively thin one of the layers.
Bio: Yury Stepanyants graduated in 1973 with the HD of MSc Diploma from the Gorky State University (Russia) and started to work as the Engineer with the Research Radiophysical Institute in Gorky. He proceeded his career with the Institute of Applied Physics of the Russian Academy of Sciences (Nizhny Novgorod) from 1977 to 1997. In 1983 Yury obtained a PhD in Physical Oceanography, and in 1992 he obtained a degree of Doctor of Sciences in Geophysics. After immigration in Australia in 1998, Yury worked for 12 years as the Senior Research Scientist with the Australian Nuclear Science and Technology Organisation in Sydney. Since July 2009 he holds a position of Full Professor at the University of Southern Queensland in Toowoomba, Australia. Yury has published more than 100 journal papers, three books, several review papers and has obtained three patents.
8 April 2021
Adam Piggott, Australian National University & Murray Elder, University of Technology Sydney
Seminar title: Recent progress on the effective Mordell problem
Elder Abstract: The growth function of a finitely generated group is a powerful and well-studied invariant. Gromov’s celebrated theorem states that a group has a polynomial growth function if and only if the group is ‘virtually nilpotent’. Of interest is a variant called the ‘geodesic growth function’ which counts the number of minimal-length words in a group with respect to some finite generating set. I will explain progress made towards an analogue of Gromov’s theorem in this case.
I will start by defining all of the terms used in this abstract (finitely generated group; growth function; virtual property of a group; nilpotent) and then give some details of the recent progress made. The talk is based on the papers arxiv.org/abs/1009.5051, arxiv.org/abs/1908.07294 and arxiv.org/abs/2007.06834 by myself, Alex Bishop, Martin Brisdon, José Burillo and Zoran Šunić.
18 March 2021
Jared M. Field, University of Melbourne
Seminar title: Gamilaraay Kinship Dynamics
Indeed, the Gamilaraay system dynamically trades off kin avoidance to minimise incidence of recessive diseases against pairwise cooperation, as understood formally through Hamilton’s rule.
Bio:Jared Field completed his undergraduate studies at the University of Sydney in Mathematics and French literature, before reading for a DPhil in Mathematical Biology at Balliol College, Oxford. He is now a McKenzie Fellow in the School of Mathematics and Statistics at the University of Melbourne, with broad interests at the intersection of mathematics, evolution and ecology.
26 February 2021
Monica Nevins, University of Ottawa
Seminar title: Recent progress on the effective Mordell problem
In this talk, I will aim to share the spirit of, and open questions in, the representation theory of G, through the lens of restricting these representations to maximal compact open subgroups.
Our point of departure: the Bruhat-Tits building of G, a 50-year-old combinatorial and geometric object that continues to reveal secrets about the structure and representation theory of G today.
9 December 2020
Minhyong Kim, University of Warwick
Seminar title: Recent progress on the effective Mordell problem
genus at least two have only finitely many rational points. This can be understood as
the statement that most polynomial equations (in a precise sense)
of degree at least 4 have at most finitely many solutions. However, the effective
version of this problem, that of constructing an algorithm for listing all rational
solutions, is still unresolved. To get a sense of the difficulty, recall how long it
took to prove that there are no solutions to
other than the obvious ones. In this talk, I will survey some of the recent progress on
an approach to this problem that proceeds by encoding rational solutions into arithmetic
principal bundles and studying their moduli in a manner reminiscent of geometric gauge
18 November 2020
Aidan Sims, University of Wollongong
Seminar title: Homotopy of product systems, K-theory of k-graph algebras, and the Yang-Baxter equations
Each k-graph can be described in terms of a coloured graph, called its skeleton, and some factorisation rules that describe how 2-coloured paths pair up into commuting squares. C*-algebras of k-graphs generalise Cuntz-Krieger algebras, and have been the subject of sustained interest essentially because questions about crossed products of C*-algebras by higher-rank free abelian groups are hard, and k-graph algebras constitute a comparably tractable class of examples that could point the way to general theorems.
A particularly obstinate question in this vein is that of determining the K-theory of a k-graph algebra, or even just whether the K-theory depends on the factorisation rules, or only on the skeleton. I’ll outline some joint work with James Fletcher and Elizabeth Gillaspy that uses a homotopy argument to establish a surprising link between this question and the question of connectedness (or otherwise) of the space of solutions to a Yang-Baxter-like equation. I won’t assume any background about C*-algebras, k-graphs, or the Yang-Baxter equations, and all are welcome—and people who might know about connectedness (or otherwise) of the spaces of solutions to Yang-Baxter-like equations are especially welcome!
11 November 2020
David Robertson, University of New England
Seminar title: Piecewise full groups of homeomorphisms of the Cantor set
They first appeared in the work of Giordano, Putnam and Skau in the context of Cantor minimal systems. Recently they have received significant attention as a source of new examples of finitely generated infinite simple groups. I will present a number of results about these groups obtained in joint work with Alejandra Garrido and Colin Reid.
28 October, 4 November 2020
James Borger and Lance Gurney, Australian National University
Series title: The geometric approach to cohomology
26 October 2020
Peng Shan, Tsinghua University
Seminar title: Coherent categorification of quantum loop sl(2)
21 October 2020
Anthony Licata, Australian National University
Seminar title: Stability conditions and automata
8 October 2020
Shamgar Gurevich, University of Wisconsin, Madison
Seminar title: Harmonic analysis on GLₙ over finite fields
Recently, we discovered that for classical groups G over finite fields there is a natural invariant of representations that provides strong information on the character ratio. We call this invariant rank.
Rank suggests a new organization of representations based on the very few “Small” ones. This stands in contrast to Harish-Chandra’s “philosophy of cusp forms”, which is (since the 60s) the main organization principle, and is based on the (huge collection) of “Large” representations.
This talk will discuss the notion of rank for the group GLₙ over finite fields, demonstrate how it controls the character ratio, and explain how one can apply the results to verify mixing time and rate for random walks.
This is joint work with Roger Howe (Yale and Texas A&M). The numerics for this work was carried with Steve Goldstein (Madison) and John Cannon (Sydney).
4 August 2020
Sam Raskin, University of Texas at Austin
Seminar title: Tate’s thesis in the de Rham setting
6 July 2020
Eugen Hellmann, University of Münster
Seminar title: On the derived category of the Iwahori–Hecke algebra
25 June 2020
Victor Ostrik, University of Oregon
Seminar title: Incompressible symmetric tensor categories
3 June 2020
David Ben-Zvi, University of Texas at Austin
Seminar title: Boundary conditions and hamiltonian actions in geometric Langlands
26 February–11 March 2020
Tom Bridgeland, University of Sheffield
Series title: Introduction to derived categories of coherent sheaves
30 January 2020
Nancy Reid, University of Toronto
Colloquium title: In praise of small data
Bio: Nancy Reid is University Professor and Canada Research Chair in Statistical Theory and Applications at the University of Toronto. Her research interests include statistical theory, likelihood inference, design of studies, and statistical science in public policy. Her main research contributions have been to the field of theoretical statistics. Professor Reid is a Fellow of the Royal Society, the Royal Society of Canada, the American Association for the Advancement of Science, and a Foreign Associate of the National Academy of Sciences. In 2014 she was appointed Officer of the Order of Canada.