Difference between revisions of "NTSGrad Fall 2020/Abstracts"

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| bgcolor="#F0A0A0" align="center" style="font-size:125%" | '''Yu Fu'''
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| bgcolor="#F0A0A0" align="center" style="font-size:125%" | '''Peter Wei'''
 
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| bgcolor="#BCD2EE"  align="center" | ''Belyi’s Theorem and Grothendieck’s dessins d’enfants (children’s drawings)''
 
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Belyi’s theorem claims that a complex smooth projective curve X can be defined over a number field, if and only if, there exists a non-constant morphism from X to P^1 as a branched cover with at most three ramification locus. The term dessins d’enfants was coined by Grothendieck in Esquisse d’un programme where he started studying dessins with the knowledge of the “obvious” if part of Belyi’s theorem. I will sketch most of the proof of Belyi’s theorem. If time permits, I will talk more about how Grothendieck was inspired by Belyi’s theorem and the subsequent studies of the faithful action of absolute Galois group Gal(Q^{\bar}/Q) on dessins.
 
Belyi’s theorem claims that a complex smooth projective curve X can be defined over a number field, if and only if, there exists a non-constant morphism from X to P^1 as a branched cover with at most three ramification locus. The term dessins d’enfants was coined by Grothendieck in Esquisse d’un programme where he started studying dessins with the knowledge of the “obvious” if part of Belyi’s theorem. I will sketch most of the proof of Belyi’s theorem. If time permits, I will talk more about how Grothendieck was inspired by Belyi’s theorem and the subsequent studies of the faithful action of absolute Galois group Gal(Q^{\bar}/Q) on dessins.
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== Nov 3 ==
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| bgcolor="#F0A0A0" align="center" style="font-size:125%" | '''Owen Goff'''
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| bgcolor="#BCD2EE"  align="center" | ''The Significance of 431: Smoothness, Unexpected Bounds, and the Unsolved Sequence''
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This talk will cover a seemingly very simple idea that connects to several branches of mathematics -- how do you write numbers as the sum of other numbers that are of the form $2^a3^b$? This talk is somewhat combinatorial in nature and references a few unsolved or recently solved problems.
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== Nov 10 ==
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| bgcolor="#F0A0A0" align="center" style="font-size:125%" | '''Ruofan Jiang'''
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| bgcolor="#BCD2EE"  align="center" | ''Crystals''
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(This was meant to be a preparation talk for Ziquan Yang happened several weeks ago, but unfortunately I didn’t make it.)
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I will tell two stories pertaining to crystals.
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1. (In char 0) crystals as an alternative way to view algebraic connections.
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2.(In char p) resolving the pathology of l-adic cohomology theory when l=p.
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The intersection of two stories is the theory of crystalline cohomology, which usually contains more arithmetic information than the usual l-adic cohomology theory, and plays an important role in many arithmetic questions.
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I will focus more on motivating ideas rather than going into details.
 
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Latest revision as of 13:30, 9 November 2020

This page contains the titles and abstracts for talks scheduled in the Fall 2020 semester. To go back to the main GNTS page, click here.


Sep 15

Qiao He
Local Arithmetic Siegel-Weil Formula at Ramified Prime
In this talk, I will describe a local arithmetic Siegel-Weil formula which relates certain intersection number on U(1,1) Rapoport-Zink space with local density. Via p-adic uniformization, this can be used to establish a global Siegel-Weil formula. The main novelty of this work is that we consider the ramified case. This is a joint work with Yousheng Shi and Tonghai Yang.


Sep 22

Johnny Han
Bounding Numbers Fields up to Discriminant

For those interested in arithmetic statistics, I'll present a quick proof of Schmidt's bound on numbers fields of given degree and bounded discriminant, as well as giving a quick overview of recent improvements on this bound by Ellenberg and Venkatesh.


Sep 29

Brandon Boggess
Dial M_{1,1} for moduli

We'll try to give a brief introduction to moduli problems, with an eye towards moduli of elliptic curves.


Oct 6

Eiki Norizuki
Character Ratio of the Transvection in GL_n(F_q)

This will be a prep talk for Wednesday's NTS talk by Shamgar Gurevich. We will talk about the character ratio of the transvection in GL_n(F_q) and results concerning this quantity.

Oct 13

Di Chen
Recent applications of geometry of numbers.

I will review geometry of numbers and then discuss its applications to bounds of 2-torsion in class groups of number fields (2017) in detail. If time permits, I will also discuss its application to counting number fields with bounded discriminant (2019) briefly.

Oct 20

Yu Fu
Representation stability and the Cohen- Lenstra Conjecture.

I will talk about the tool of representation stability in cohomology and how can one use this to do some algebraic counting over finite field, how it works in the proof of the Cohen- Lenstra conjecture over function field in Jordan's 2015 paper if time permits.


Oct 27

Peter Wei
Belyi’s Theorem and Grothendieck’s dessins d’enfants (children’s drawings)

Belyi’s theorem claims that a complex smooth projective curve X can be defined over a number field, if and only if, there exists a non-constant morphism from X to P^1 as a branched cover with at most three ramification locus. The term dessins d’enfants was coined by Grothendieck in Esquisse d’un programme where he started studying dessins with the knowledge of the “obvious” if part of Belyi’s theorem. I will sketch most of the proof of Belyi’s theorem. If time permits, I will talk more about how Grothendieck was inspired by Belyi’s theorem and the subsequent studies of the faithful action of absolute Galois group Gal(Q^{\bar}/Q) on dessins.

Nov 3

Owen Goff
The Significance of 431: Smoothness, Unexpected Bounds, and the Unsolved Sequence

This talk will cover a seemingly very simple idea that connects to several branches of mathematics -- how do you write numbers as the sum of other numbers that are of the form $2^a3^b$? This talk is somewhat combinatorial in nature and references a few unsolved or recently solved problems.

Nov 10

Ruofan Jiang
Crystals

(This was meant to be a preparation talk for Ziquan Yang happened several weeks ago, but unfortunately I didn’t make it.)

I will tell two stories pertaining to crystals.

1. (In char 0) crystals as an alternative way to view algebraic connections.

2.(In char p) resolving the pathology of l-adic cohomology theory when l=p.

The intersection of two stories is the theory of crystalline cohomology, which usually contains more arithmetic information than the usual l-adic cohomology theory, and plays an important role in many arithmetic questions.

I will focus more on motivating ideas rather than going into details.