When: Thursday 5:006:00 PM CST
Where: https://uwmadison.zoom.us/j/92877740706?pwd=OVo0QmxRVEdUQ3RnUWpoWmFRRUI3dz09
Lizzie the OFFICIAL mascot of GAGS!!
Who: All undergraduate and graduate students interested in algebraic geometry, commutative algebra, and related fields are welcome to attend.
Why: The purpose of this seminar is to learn algebraic geometry and commutative algebra by giving and listening to talks in a informal setting. Talks are typically accessible to beginning graduate students and take many different forms. Sometimes people present an interesting paper they find. Other times people give a prep talk for the Friday Algebraic Geometry Seminar. Other times people give a series of talks on a topic they have been studying indepth. Regardless the goal of GAGS is to provide a supportive and inclusive place for all to learn more about algebraic geometry and commutative algebra.
How: If you want to get emails regarding time, place, and talk topics (which are often assigned quite last minute) add yourself to the gags mailing list: gags@lists.wisc.edu. The list registration page is here.
Give a talk!
We need volunteers to give talks this semester. If you're interested contact Colin or David, or just add yourself to the list (though in that case we might move your talk later without your permission). Beginning graduate students are particularly encouraged to give a talk, since it's a great way to get your feet wet with the material.
Being an audience member
The goal of GAGS is to create a safe and comfortable space inclusive of all who wish to expand their knowledge of algebraic geometry and commutative algebra. In order to promote such an environment in addition to the standard expectations of respect/kindness all participants are asked to following the following guidelines:
 Do Not Speak For/Over the Speaker:
 Ask Questions Appropriately:
Spring 2021
February 4
Asvin Gothandaraman

Title: A Bertini type theorem via probability

Abstract: I will prove that most hyperplane slices are irreducible over any field by reducing to finite fields and applying probabilistic arguments. The talk will be very elementary!

February 25
Colin Crowley

Title: TBD

Abstract: TDB

March 11
Roufan Jiang

Title: TBD

Abstract: TBD

March 18
Alex Hof

Title: An Introduction to the Deformation Theory of Complete Intersection Singularities

Abstract: Essentially what it says in the title; I'll give a fairly laidback overview of some of the basic definitions and results about deformations of complete intersection singularities, including the KodairaSpencer map and the existence of versal deformations in the isolated case. If time permits, I'll discuss Morsification of isolated singularities. Very little background will be assumed.

March 25
Chiahui (Wendy) Cheng

Title: Explicit Bound on Collective Strength of Regular Sequences of Three Homogeneous Polynomials

Abstract: Let f_1,...,f_r in k[x_1,...,x_n] be homogeneous polynomial of degree d. Ananyan and Hochster (2016) proved that there exists a bound N=N(r,d) where if collective strength of f_1,...,f_r is greater than or equal to N, then f_1,...,f_r are regular sequence. In this paper, we study the explicit bound N(r,d) when $r=3$ and d=2,3 and show that N(3,2)=2 and N(3,3)>2.

April 1
Erika Pirnes

Title: Reconstruction conjecture in graph theory (Note: special time at noon!)

Abstract: The deck of a graph with n vertices is a multiset of n unlabeled graphs, each obtained from the original graph by deleting a vertex (and the edges incident to it). The reconstruction conjecture says that if two finite simple graphs with at least three vertices have the same deck, then they are isomorphic. The talk is going to focus on examples, and does not assume previous knowledge about graph theory.

April 8
Caitlyn Booms

Title: TBD

Abstract: TBD

April 29
Owen Goff

Title: TBD

Abstract: TBD

Fall 2020
Spring 2020
January 29
Colin Crowley

Title: Lefschetz hyperplane section theorem via Morse theory

Abstract: Morse theory allows you to learn about the topology of a manifold by studying the critical points of a nice function on the manifold. This perspective produces a nice proof of the theorem in the title, which concerns the homology of smooth projective varieties over C. I'll explain what the theorem says, say something about what Morse theory is and why it's related, and then finish with a neat example. I'm aiming to make this understandable to someone who's taken algebraic geometry 1 and topology 1.

February 5
Asvin Gothandaraman

Title: An introduction to unirationality

Abstract: I will introduce the notion of unirationality and show that cubic hypersurfaces are unirational (following Kollar). If time permits, I will also show that unirational varieties are simply connected.

February 12
February 19
Dima Arinkin

Title: Blowing down, blowing up: surface geometry

Abstract:A big question in algebraic geometry is how much one can change a variety without affecting it `generically'. More precisely, if two varieties are birational, how far can they be from being isomorphic?
The question is trivial for (smooth projective) curves: they are birational if and only if they are isomorphic. In higher dimension, the
situation is much more interesting. The most fundamental operation are the `blowup', which is a kind of alteration of a variety within its birational isomorphism class, and its opposite, the blowdown.
In my talk, I will introduce blowups and discuss their properties. Then (time permitting) I would like to look deeper at the case
of surfaces, where the combination of blowups and intersection theory provides a complete and beautiful picture. (If we do get to this point, I won't assume any knowledge of intersection theory: to an extent, this talk is my excuse to introduce it.)

February 26
Connor Simpson

Title: Intro to Toric Varieties

Abstract: A brief introduction to toric varieties: how to build them, formulas for computing topological data, toric blowups, and more.

March 4
Peter Wei

Title: An introduction to GrothendieckRiemannRoch Theorem

Abstract: The classical RiemannRoch theorem tells you about how topological (genus) and analytical (through line bundle) properties on compact Riemann surface (i.e. smooth projective curve) relate to each other. Moreover, this theorem can be generalized to any vector bundles (or coherent sheaves) over any smooth projective varieties. Eventually, Grothendieck “relativized” this theorem as a property of a morphism between two projective varieties. In this talk I will introduce basic notions to formulate this theorem. If time permitting, enough examples will be given appropriately.

March 11
Caitlyn Booms

Title: Intro to StanleyReisner Theory

Abstract: StanleyReisner theory gives a dictionary between combinatorial objects (simplicial complexes) and algebraic objects (StanleyReisner rings). In this talk, I will introduce the main objects of study in this theory, describe this dictionary with several examples, and discuss how StanleyReisner theory can help us investigate algebrageometric questions.

March 25
Steven He

Title: Braid group action on derived category

Abstract: In this talk, I will define spherical object and A_mconfiguration in derived category of coherent sheaves, and say a few words about the motivation coming from the homological mirror symmetry.

April 1
Vlad Sotirov

Title:

Abstract:

April 8
Maya Banks

Title:

Abstract:

April 15
Alex Hof

Title: Embrace the Singularity: An Introduction to Stratified Morse Theory

Abstract: Early on in the semester, Colin told us a bit about Morse
Theory, and how it lets us get a handle on the (classical) topology of
smooth complex varieties. As we all know, however, not everything in
life goes smoothly, and so too in algebraic geometry. Singular
varieties, when given the classical topology, are not manifolds, but
they can be described in terms of manifolds by means of something called
a Whitney stratification. This allows us to develop a version of Morse
Theory that applies to singular spaces (and also, with a bit of work, to
smooth spaces that fail to be nice in other ways, like noncompact
manifolds!), called Stratified Morse Theory. After going through the
appropriate definitions and briefly reviewing the results of classical
Morse Theory, we'll discuss the socalled Main Theorem of Stratified
Morse Theory and survey some of its consequences.

April 22
Ruofan

Title: Birational geometry: existence of rational curves

Abstract: Rational curves on a variety control its birational geometry. It thus is important to determine whether they exist. People didn’t know how to do this systematically, before Mori discovered a deformation lemma which detect their existence, and bound their degree if they exist. I will briefly introduce Mori’s insight.

April 29
John Cobb

Title:

Abstract:

Organizers' Contact Info
Colin Crowley
David Wagner
The List of Topics that we Made February 2018
On February 21st of the Month of February of The 2018th Year of the Seventh Age of The Sun, the People Present at GAGS Compiled Ye Followinge Liste of Topics They Wished to Hear Aboute:
Feel free to edit the list and/or add references to learn this stuff from. Since then, we've succeeded in talking about some of these, which doesn't mean there shouldn't be another talk. Ask around or look at old semester's websites.
 Schubert Calculus, aka how many lines intersect four given lines in threedimensional space? The answer to this question is prettiest when you think about it as a problem of intersecting subvarieties in the Grassmanian. What is the Grassmanian, you say? That's probably a talk we should have every year, so you should give it!
 Kindergarten GAGA. GAGA stands for Algebraic Geometry  Analytic Geometry. Serre wrote a famous paper explaining how the two are related, and you could give an exposition suitable to kindergardeners.
 Katz and Mazur explanation of what a modular form is. What is it?
 Kindergarten moduli of curves.
 What is a dualizing sheaf? What is a dualizing complex? What is Serre duality? What is local duality? Can local duality help us understand Serre duality?
 Generalizations of Riemann  Roch. (Grothendieck  Riemann  Roch? Hirzebruch  Riemann  Roch?)
 What and why is a dessin d'enfants?
Ed Dewey's Wish List Of Olde
Back in the day Ed and Nathan made this list of topics they wanted to hear. They all sound super duper cool, but it's also true that they had many years of AG behind their backs, so this list might not be very representative of what the GAGS audience wants to hear bout.
Here are the topics we're DYING to learn about! Please consider looking into one of these topics and giving one or two GAGS talks.
Specifically Vague Topics
 Dmodules 101: basics of Dmodules, equivalence between left and right Dmodules, pullbacks, pushforwards, maybe the GaussManin Connection. Claude Sabbah's introduction to the subject could be a good place to start.
 Sheaf operations on Dmodules (the point is that then you can get a FourierMukai transform between certain Omodules and certain Dmodules, which is more or less how geometric Langlands is supposed to work)
Interesting Papers & Books
 Symplectic structure of the moduli space of sheaves on an abelian or K3 surface  Shigeru Mukai.
 Residues and Duality  Robin Hatshorne.
 Have you heard of Serre Duality? Would you like to really understand the nuts and bolts of it and its generalizations? If so this book is for you. (You wouldn't need to read the whole book to give a talk ;).)
 Coherent sheaves on P^n and problems in linear algebra  A. A. Beilinson.
 In this two page paper constructs the semiorthogonal decomposition of the derived category of coherent sheaves on projective space. (This topic is very important, and there are a ton of other resources for this result and the general theory of derived categories.)
 Frobenius splitting and cohomology vanishing for Schubert varieties  V.B. Mehta and A. Ramanathan.
 In characteristic p the fact that (x+y)^p=x^p+y^p means that one has the Frobenius morphism, which sends f to f^p. In this paper the authors introduce the notion of what it means for a variety to be Frobenius split, and use this to prove certain cohomologcal vanishing results for Schubert varieties. Since then Frobenius splitting  and its related cousins (Fregularity, strong Fregularity, Fpurity, etc.) have played large roles in geometry and algebra in characteristic p. This is a good place to get a sense for what kicked all this stuff off!
 Schubert Calculus  S. L. Kleiman and Dan Laksov.
 An introduction to Schubert calculus suitable for those of all ages. I am told the paper essentially only uses linear algebra!
 Rational Isogenies of Prime Degree  Barry Mazur.
 In this paper Mazur classifies all isogenies of rational elliptic curves of prime order. As a result of this he deduces his famous result that the torsion subgroup of an elliptic curve (over Q) is one of 15 abelian groups. This definitely stares into the land of number theory, but certainly would still be of interest to many.
 Esquisse d’une programme  Alexander Grothendieck.
 Originating from a grant proposal in the mid 1980's this famous paper outlines a tantalizing research program, which seeks to tie numerous different areas of math (algebraic geometry, Teichmuller theory, Galois theory, etc.) together. This is where Grothendieck introduced his famous Lego game and dessin d'enfant. While just a research proposal this paper has seemingly inspired a ton of cool math, and will allow you to "blow peoples’ minds". (The original paper is in French, but there are English translations out there.)
 Géométrie algébraique et géométrie analytique  J.P. Serre.
 A projective variety X over the complex numbers has two lives, an algebraic and an analytic, depending on which topology one wishes to work with. That is one can think about X as a complex manifold and work with holomorphic functions or as an algebraic variety and work with regular functions. Hence to any complex projective variety we have two sheaf theories and as a result two cohomology theories. In this famous paper Serre compares these two and shows they are in fact the same. (Note: This is a super fundamental result that is used all the time; normally in the following way: Uhh... What do you mean by cohomology? Well by GAGA or something it doesn't really mater.) (The original paper is in French, but there are English translations out there.)
 Limit linear series: Basic theory David Eisenbud and Joe Harris.
 One of the more profitable tools  especially when studying moduli spaces  in a geometers tool box is the theory of degenerations. However, sometimes we care about more than just the variety we are degenerating and want to keep track of things like vector/line bundles. In this paper Eisenbud and Harris develop the theory of degenerating a curve together with a linear series. From this they prove a ton of cool results: M_g is of general type for g>24, BrillNoether theory, etc.
 Picard Groups of Moduli Problems  David Mumford.
 This paper is essentially the origin of algebraic stacks.
 The Structure of Algebraic Threefolds: An Introduction to Mori's Program  Janos Kollar
 This paper is an introduction to Mori's famous ``minimal model program, which is a far reaching program seeking to understand the birational geometry of higher dimensional varieties.
 CayleyBacharach Formulas  Qingchun Ren, Jürgen RichterGebert, Bernd Sturmfels.
 A classical result we all learn in a first semester of algebraic geometry is that 5 points in the plane (in general position) determine a unique plane conic. One can similarly show that 9 (general) points in the plane determine a unique plane cubic curve. This paper tries to answer the question: ``What is equation for this cubic curve?.
 On Varieties of Minimal Degree (A Centennial Approach)  David Eisenbud and Joe Harris.
 Suppose X is a projective variety embedded in projective space so that X is not contained in any hyperplane. By projecting from general points one can see that the degree of X is at least codim(X)+1. This paper discusses the classification of varieties that achieve this lower degree bound i.e. varieties of minimal degree. This topic is quite classical and the paper seems to contain a nice mixture of classical and modern geometry.
 The GromovWitten potential associated to a TCFT  Kevin J. Costello.
 This seems incredibly interesting, but fairing warning this paper has been described as highly technical, which considering it uses Ainfinity algebras and the derived category of a CalabiYau seems like a reasonable description. (This paper may be covered in Caldararu's Spring 2017 topics course.)
Past Semesters
Fall 2019
Spring 2019
Fall 2018
Spring 2018
Fall 2017
Spring 2017
Fall 2016
Spring 2016
Fall 2015