Department of

Mathematics


Seminar Calendar
for Topology events the year of Monday, April 16, 2018.

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More information on this calendar program is available.
Questions regarding events or the calendar should be directed to Tori Corkery.
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Friday, January 19, 2018

4:00 pm in 241 Altgeld Hall,Friday, January 19, 2018

Organizational Meeting

Abstract: We'll get the schedule of talks for the semester worked out. There will be cookies.

Friday, January 26, 2018

4:00 pm in 241 Altgeld Hall,Friday, January 26, 2018

Ice cream geometry: a mathematical activity and coloring book

Melinda Lanius (UIUC)

Abstract: Come explore metrics I use in my dissertation research. In a souped-up color-by-numbers, we'll develop a general notion of circle and ball. In geodesic connect-the-dots, we'll see what happens when straight lines curve. In metric mazes, we'll come to appreciate the wonky ways of nonhomogeneous spaces. After exploring the geometries of the real and hyperbolic plane, sphere, cone, and cylinder, we'll conclude by building less familiar objects: surfaces with a Euclidean, cylindrical, conical, or hyperbolic-funnel end. Please bring your fun office supplies!

Tuesday, January 30, 2018

11:00 am in 345 Altgeld Hall,Tuesday, January 30, 2018

Localizing the E_2 page of the Adams spectral sequence

Eva Belmont (MIT)

Abstract: The Adams spectral sequence is one of the central tools for calculating the stable homotopy groups of spheres, one of the motivating problems in stable homotopy theory. In this talk, I will discuss an approach for computing the Adams E_2 page at p = 3 in an infinite region, by computing its localization by the non-nilpotent element b_{10}. This approach relies on computing an analogue of the Adams spectral sequence in Palmieri's stable category of comodules, which can be regarded as an algebraic analogue of stable homotopy theory. This computation fits in the framework of chromatic homotopy theory in the stable category of comodules.

Friday, February 2, 2018

4:00 pm in 241 Altgeld Hall,Friday, February 2, 2018

Integrable systems in algebraic geometry

Matej Penciak (UIUC)

Abstract: In this talk I'll introduce the definition of an algebraic integrable system. The definition axiomatizes what it means to have an integrable system in algebraic geometry. After connecting the definition to the more common notion in differential geometry, I'll give a few examples of my favorite integrable systems. Possible examples are the Hitchin system on the space of Higgs bundles, the Calogero-Moser system, the Toda lattice hierarchy, and, if time permits, I'll try to give a hint of how all these systems are related via the gauge theory in physics.

Friday, February 9, 2018

4:00 pm in 241 Altgeld Hall,Friday, February 9, 2018

What are spectra?

Tsutomu Okano (UIUC)

Abstract: This is an introductory talk on stable homotopy theory. I will begin by discussing stable phenomena in homotopy theory that led to the definition of spectra. Spectra represent generalized cohomology theories, such as various kinds of K-theories and cobordism theories. This implies that results about cohomology theories can be proven in the category of spectra, using analogies from topological spaces. Unfortunately, the earlier category of spectra was defective in formal properties and it was not until the 1990's that suitable categories of spectra were defined. This formality leads to the study of other sorts of homotopy theories, such equivariant and motivic homotopy theories.

Tuesday, February 13, 2018

11:00 am in 345 Altgeld Hall,Tuesday, February 13, 2018

Factorization homology and topological Hochschild cohomology of Thom spectra

Inbar Klang (Stanford)

Abstract: By a theorem of Lewis, the Thom spectrum of an n-fold loop map to BO is an E_n-ring spectrum. I will discuss a project studying the factorization homology and the E_n topological Hochschild cohomology of such Thom spectra, and talk about some applications, such as computations, and a duality between topological Hochschild homology and cohomology of certain Thom spectra. Time permitting, I will discuss connections to topological field theories. This talk will include an introduction to factorization homology via labeled configuration spaces.

Friday, February 16, 2018

4:00 pm in 241 Altgeld Hall,Friday, February 16, 2018

Canceled

(UIUC)

Wednesday, February 21, 2018

12:00 pm in 443 Altgeld Hall,Wednesday, February 21, 2018

Bounding Betti numbers of patchworked real hypersurfaces by Hodge numbers

Kristin Shaw (MPI Leipzig)

Abstract: The Smith-Thom inequality bounds the sum of the Betti numbers of a real algebraic variety by the sum of the Betti numbers of its complexification. In this talk I will explain our proof of a conjecture of Itenberg which refines this bound for a particular class of real algebraic projective hypersurfaces in terms of the Hodge numbers of its complexification. The real hypersurfaces we consider arise from Viro’s patchworking construction, which is a powerful combinatorial method for constructing topological types of real algebraic varieties. To prove the bounds conjectured by Itenberg, we develop a real analogue of tropical homology and use spectral sequences to compare it to the usual tropical homology of Itenberg, Katzarkov, Mikhalkin, Zharkov. Their homology theory gives the Hodge numbers of a complex projective variety from its tropicalisation. Lurking in the spectral sequences of the proof are the keys to controlling the topology of the real hypersurface produced from a patchwork. This is joint work in preparation with Arthur Renaudineau.

Friday, February 23, 2018

4:00 pm in 241 Altgeld Hall,Friday, February 23, 2018

Unoriented Bordism and the Algebraic Geometry of Homotopy Theory

Brian Shin (UIUC)

Abstract: The classification of manifolds up to bordism is an interesting geometric problem. In this talk, I will discuss how this problem connects to homotopy theory. In particular, I will demonstrate that viewing the homotopy theorist's toolbox through the lens of algebraic geometry leads naturally to the solution for the classification of manifolds up to bordism.

Tuesday, March 6, 2018

11:00 am in Psychology Building 21,Tuesday, March 6, 2018

The generalized homology of $BU\langle 2k\rangle$

Phillip Jedlovec

Abstract: In their 2001 paper, ``Elliptic spectra, the Witten genus and the theorem of the cube,'' Ando, Hopkins, and Strickland use an algebro-geometric perspective to give a partial description of the generalized homology of the connective covers of BU. For any complex-orientable cohomology theory, E, they define homology elements $b_{i_1, ..., i_k}$ in $E_*BU\langle 2k\rangle$, prove the so called ``cocycle relations'' and ``symmetry relations'' on these elements, and show that when $E=H\mathbb{Q}$ or $k=1, 2,$ or $3$, these are in fact the defining relations for $E_*BU\langle 2k\rangle$. In this talk, I will sketch a new proof of these results which uses very little algebraic geometry, but instead uses facts about Hopf rings and the work of Ravenel and Wilson on the homology of the spaces in the $\Omega$-spectrum for Brown-Peterson cohomology. Time permitting, I will also discuss how this approach might be used to prove the Ando-Hopkins-Strickland theorem for $k>3$ and $E=H\mathbb{Z}_{(2)}$.

Friday, March 9, 2018

4:00 pm in 241 Altgeld Hall,Friday, March 9, 2018

Cancelled

Friday, March 16, 2018

4:00 pm in 241 Altgeld Hall,Friday, March 16, 2018

Operations in complex K theory

William Balderrama (UIUC)

Abstract: In nice cases, the correct algebraic setup can exert a large amount of control over a geometric situation. I will illustrate this with the example of complex K theory.

Friday, March 30, 2018

4:00 pm in 241 Altgeld Hall,Friday, March 30, 2018

Optimizing mesh quality

Sarah Mousley (UIUC)

Abstract: I will talk about a project in computational geometry I worked on during a summer internship at Sandia National Lab. Our work builds on that of Mullen et al., who introduced a new energy function for meshes (triangulations) and an algorithm for finding low energy meshes. The energy is a measure of the mesh’s quality for usage in Discrete Exterior Calculus (DEC), a method for numerically solving PDEs. In DEC, the PDE domain is triangulated and this mesh is used to obtain discrete approximations of the continuous operators in the PDE. While the motivation for this work is to obtain better solutions to PDEs, do not be turned off. I didn't solve a single PDE all summer. This is a geometry talk.

Monday, April 2, 2018

4:00 pm in 245 Altgeld Hall,Monday, April 2, 2018

Why topology is geometry in dimension 3

Nathan Dunfield   [email] (Department of Mathematics, University of Illinois at Urbana-Champaign)

Abstract: After setting the stage by sketching a few facts about the topology and geometry of surfaces, I will explain why the study of the topology of 3-dimensional manifolds is inextricably linked to the study of homogenous geometries such as Euclidean, spherical, and (especially) hyperbolic geometry. This perspective, introduced by Thurston in the 1980s, was stunningly confirmed in the early 2000s by Perelman's deep work using geometric PDEs, and lead to the solution of the 100 year-old Poincaré conjecture. I will hint at how this perspective brings other areas of mathematics, specifically algebraic geometry and number theory, to bear on problems that initially appear purely topological in nature, and conclude with a live computer demonstration of how geometry can be used to tell different 3-manifolds apart in practice.

Friday, April 13, 2018

4:00 pm in 241 Altgeld Hall,Friday, April 13, 2018

What is group cohomology?

Elizabeth Tatum (UIUC)

Abstract: Group cohomology has many uses in algebra, topology, and number theory. In this talk, I will introduce group cohomology, give some basic examples, and discuss some applications to topology.

Tuesday, April 17, 2018

11:00 am in 345 Altgeld Hall,Tuesday, April 17, 2018

About Bredon motivic cohomology of a field

Mircea Voineagu

Abstract: We introduce Bredon motivic cohomology and show that complexes of equivariant equidimensional cycles compute this cohomology. We use this and other methods to identify the Bredon motivic cohomology of a field in weight 0 and 1 as well as the Bredon motivic cohomology of the field of complex numbers. This is a joint work with J. Heller and P.A. Ostvaer.

Friday, April 20, 2018

4:00 pm in 241 Altgeld Hall,Friday, April 20, 2018

The Volume Conjecture

Xinghua Gao (UIUC)

Abstract: It is a fundamental goal of modern knot theory to “understand” the Jones polynomial. The volume conjecture, which was initially formulated by Kashaev and later generalized by Murakami^2, relates quantum invariants of knots to the hyperbolic geometry of knot complements. In this talk, I will briefly explain the volume conjecture. No background in knot theory/hyperbolic geometry/physics required.

Wednesday, April 25, 2018

4:00 pm in 245 Altgeld Hall,Wednesday, April 25, 2018

Randomness in 3-Dimensional Geometry and Topology

Malik Obeidin (Illinois Math)

Abstract: The probabilistic method, pioneered by Paul Erdos, has proven to be one of the most powerful and versatile tools in the field of combinatorics. Mathematicians working in diverse fields, from graph theory to number theory to linear algebra, have found the probabilistic toolset valuable. However, 3-manifold topology has only been recently approached from this angle, though the field itself is full of intricate combinatorics. In this talk, I'll describe some of the ways one might define a "random 3-manifold" and the subtleties that arise in the definition. I'll also talk about how one can use these ideas to experiment computationally with 3-manifolds, to help us get a handle on what is "common", and what is "rare".

Friday, April 27, 2018

4:00 pm in 241 Altgeld Hall,Friday, April 27, 2018

Cannon-Thurston Maps

Elizabeth Field (UIUC)

Abstract: When a map between two objects extends to a continuous map between their boundaries, this boundary map is called the Cannon-Thurston map. When the objects at play are a hyperbolic group and a hyperbolic subgroup, there are two main questions which arise from this definition. First, when does the Cannon-Thurston map exist? Further, if such a map exists, can the fibers of this map be described in some nice algebraic or geometric way? In this talk, we will introduce the background needed to understand these questions. We will then briefly explore some of what is known about their answers, as well as some open questions which remain.

Friday, August 10, 2018

4:00 pm in Altgeld Hall,Friday, August 10, 2018

Definable topological spaces in o-minimal structures

Pablo Andujar Guerrero (Konstanz)

Abstract: In model theory a topological space can be interpreted naturally as a second order structure, namely a set and the unary relation of subsets that corresponds to the topology. A different approach is that of a first order structure in which there exists a topological space with a basis that is (uniformly) definable. We call this a definable topological space. A natural example corresponds to the order topology on any linearly ordered structure. During this talk I’ll present results on definable topological spaces in an o-minimal structure $\mathcal{R} = (R, ...)$. In particular we will classify Hausdorff definable topological spaces $(X, \tau )$ where $X \subseteq R$. We’ll consider a number of first order properties of these spaces that resemble topological properties and note how, in the o-minimal setting, the induced framework, which we might call “definable topology”, resembles general topology. This is joint work with Margaret Thomas and Erik Walsberg.

Friday, August 31, 2018

4:00 pm in Altgeld Hall 241,Friday, August 31, 2018

Organizational Meeting

Jesse Huang (UIUC)

Abstract: We will draft a schedule of the seminar talks this semester. Please join us this afternoon and sign up if you have a topic in mind. As usual, cookies will be provided. All are welcome!

Friday, September 7, 2018

4:00 pm in Altgeld Hall 241,Friday, September 7, 2018

A generalization of pair of pants decompositions

Jesse Huang (UIUC)

Abstract: We will talk about higher dimensional pair of pants decompositions for smooth projective hypersurfaces.

Tuesday, September 11, 2018

11:00 am in 345 Altgeld Hall,Tuesday, September 11, 2018

Some Plethyistic Algebra

Charles Rezk (UIUC)

Abstract: This is a talk about an algebraic notion of a plethory. A plethory P determines a category of "P-rings", objects of which are commutative rings R equipped with a collection of functions $f_i : R \to R$ satisfying a list of axioms. Many interesting cohomology theories take values in a category of P-rings for some plethory P. The motivating example is K-theory, which takes values in "Lambda-rings", which is precisely the category of rings for the Lambda plethory. This talk will be expository, concentrating first on interesting examples of P-rings, then working backward to the definition of plethory. Then I'll talk about the "Witt ring" construction associated to any plethory, which includes and generalizes the classical construction of "Witt vectors".

Friday, September 14, 2018

4:00 pm in 241 Altgeld Hall,Friday, September 14, 2018

3 invariants of manifolds you won’t believe are the same!

Hadrian Quan

Abstract: We’ll start by discussing everyone’s favorite invariant: the determinant of a linear map. After generalizing this to an invariant of a chain complex, we’ll talk about three different different ways to get a number from a representation of $\pi_1(M)$: topological, analytic, and dynamical. Number 3 might surprise you!

Monday, September 17, 2018

3:00 pm in 243 Altgeld Hall,Monday, September 17, 2018

Pre-Calabi-Yau structures and moduli of representations

Wai-kit Yeung (Indiana University)

Abstract: Pre-Calabi-Yau structures are certain structures on associative algebras introduced by Kontsevich and Vlassopoulos. This incorporates as special cases many other algebraic structures of diverse origins. Elementary examples include double Poisson algebras introduced by Van den Bergh, as well as infinitesimal bialgebras studied by Aguiar. Other examples also arise from symplectic topology as well as from string topology, whose relation with topological conformal field theory can be formulated in terms of pre-Calabi-Yau structures. In this talk, we will define pre-Calabi-Yau structures, and study it in the context of noncommutative algebraic geometry. In particular, we show that Calabi-Yau structures, introduced by Ginzburg and Kontsevich-Vlassopoulos, can be viewed as noncommutative analogue of symplectic structures. Pushing this analogy, one can show that pre-Calabi-Yau structures are noncommutative analogue of Poisson structures. As a result, we indicate how a pre-Calabi-Yau structure on an algebra induces a (shifted) Poisson structure on the moduli space of representations of that algebra.

4:00 pm in 239 Altgeld Hall,Monday, September 17, 2018

Building your own Möbius kaleidocycles

Eliot Fried (Mathematics, Mechanics, and Materials Unit, Okinawa Institute of Science and Technology Graduate University)

Abstract: Kaleidocycles are internally mobile ring linkages consisting of tetrahedra which are connected by revolute hinges. Instead of the classical, very popular, kaleidocycles with even numbers (usually six, sometimes eight) of elements, we will build kaleidocycles with seven or nine elements and several different surface designs. Moreover, we will learn that it is possible to construct kaleidocycles with any number of elements greater than or equal to six. These new kaleidocycles have two novel properties: they have only a single degree of freedom and they have the topology of a Möbius band.

Tuesday, September 18, 2018

11:00 am in 345 Altgeld Hall,Tuesday, September 18, 2018

Unstable $v_1$-periodic Homotopy Groups through Goodwillie Calculus

Jens Kjær (Notre Dame Math)

Abstract: It is a classical result that the rational homotopy groups, $\pi_*(X)\otimes \mathbb{Q}$, as a Lie-algebra can be computed in terms of indecomposable elements of the rational cochains on $X$. The closest we can get to a similar statement for general homotopy groups is the Goodwillie spectral sequence, which computes the homotopy group of a space from its "spectral Lie algebra". Unfortunately both input and differentials are hard to get at. We therefore simplify the homotopy groups by taking the unstable $\nu_h$-periodic homotopy groups, $\nu_h^{-1}\pi_*(\ )$ (note $h=0$ recovers rational homotopy groups). For $h=1$ we are able to compute the $K$-theory based $\nu_1$-periodic Goodwillie spectral sequence in terms of derived indecomposables. This allows us to compute $\nu_1^{-1}\pi_*SU(d)$ in a very different way from the original computation by Davis.

4:00 pm in 245 Altgeld Hall ,Tuesday, September 18, 2018

Möbius kaleidocycles: a new class of everting ring linkages

Eliot Fried (Mathematics, Mechanics, and Materials Unit, Okinawa Institute of Science and Technology Graduate University)

Abstract: Many of Escher’s works have become mainstays of popular culture. Famous examples include his Möbius bands and kaleidocycles. Made from six identical regular tetrahedra joined by revolute hinges, a kaleidocycle possesses a single internal degree-of-freedom that is manifested by a cyclic everting motion that brings different faces of the tetrahedra into view. We will describe "Möbius Kaleidocycles," a previously undiscovered class ring linkages made from seven or more identical links joined by revolute hinges. For each number of links, there exists a specific twist angle between neighboring hinges for which the associated Möbius Kaleidocycle possesses only a single internal degree-of-freedom, allowing for cyclic eversion, and the hinge orientations induce a nonorientable topology equivalent to that of a 3π twist Möbius band. Apart from technological applications, including perhaps the design of new organic ring molecules with peculiar electronic properties, Möbius kaleidocycles generate a myriad of intriguing questions in geometry and topology, some of which will be addressed in this talk. This is joint work with postdoctoral scholar Johannes Schönke.

Thursday, September 20, 2018

12:00 pm in 243 Altgeld Hall,Thursday, September 20, 2018

The generalization of the Goldman bracket to three manifold and its relation to Geometrization

Moira Chas (Stony Brook)

Abstract: In the eighties, Bill Goldman discovered a Lie algebra structure on the free abelian group with basis the free homotopy classes of closed oriented curves on an oriented surface S. In the nineties, jointly with Dennis Sullivan, we generalized this Lie algebra structure to families of loops (defining the equivariant homology of the free loop space of a manifold). This Lie algebra, together with other operations in spaces of loops is now known as String Topology. The talk will start with a discussion of the Goldman Lie bracket in surfaces, and how it "captures" the geometric intersection number between curves. It will continue with the description of the string bracket, which generalizes of the Goldman bracket to oriented manifolds of dimension larger than two, and the space of families of loops where the string bracket is defined. The second part of the lecture describes how this structure in degrees zero and one plus the power operations in degree zero recognizes key features of the Geometrization, the above mentioned joint work. The lions share of effort concerns the torus decomposition of three manifolds which carry mixed geometry. This is joint work with Siddhartha Gadgil and Dennis Sullivan.

4:00 pm in 245 Altgeld Hall,Thursday, September 20, 2018

Computer Driven Questions, Theorems and Pre-theorems in Low Dimensional Topology

Moira Chas (Stony Brook University)

Abstract: Consider an orientable surface S with negative Euler characteristic, a minimal set of generators of the fundamental group of S, and a hyperbolic metric on S. Then each unbased homotopy class C of closed oriented curves on S determines three numbers: the word length (that is, the minimal number of letters needed to express C as a cyclic word in the generators and their inverses), the minimal geometric self-¬intersection number, and finally the geometric length. Also, the set of free homotopy classes of closed directed curves on S (as a set) is the vector space basis of a Lie algebra discovered by Goldman. This Lie algebra is closely related to the intersection structure of curves on S. These three numbers, as well as the Goldman Lie bracket of two classes, can be explicitly computed (or approximated) using a computer. These computations led us to counterexamples to existing conjectures, to formulate new conjectures and (sometimes) to subsequent theorems.

Friday, September 21, 2018

4:00 pm in 241 Altgeld Hall,Friday, September 21, 2018

The geometry of some low dimensional Lie groups

Ningchuan Zhang (UIUC)

Abstract: In this talk, I'll give explicit geometric descriptions of some low dimensional matrix groups. The goal is to show $\mathrm{SU}(2)\simeq S^3$ is a double cover of $\mathrm{SO}(3)$ and $\mathrm{SL}_2(\mathbb{C})$ is a double cover of the Lorentz group $\mathrm{SO}^+(1,3)$. Only basic knowledge of linear algebra and topology is assumed.

Tuesday, September 25, 2018

11:00 am in 345 Altgeld Hall,Tuesday, September 25, 2018

To Be Announced

Egbert Rijke (UIUC)

Abstract: TBA

Tuesday, October 9, 2018

11:00 am in 345 Altgeld Hall,Tuesday, October 9, 2018

To Be Announced

Piotr Pstrągowski (Northwestern Math)

Abstract: TBA