AGNT seminar 2020

Organizers: Anders Södergren, Christian Johansson.

Upcoming seminars

Note​: For the time being, all upcoming seminars will be online. Please check the calendar

for information on how to join, or email one of the organizers. The standard time for the seminars in Autumn 2020 is 15.15-16.15. However, there are exceptions --- please check the calendar above or email one of the organizers for information about the time.

07.10.2020 - Jack Shotton (University of Durham): TBA

21.10.2020 - Peter Sarnak (Princeton University/Institute for Advanced Study): TBA

28.10.2020 - Scott Ahlgren (University of Illinois, Urbana-Champaign): TBA ---  OBS! 14.30-15.30

04.11.2020 - John Christian Ottem (University of Oslo): TBA

18.11.2020 - Tim Browning (IST Austria): TBA​

02.12.2020 - Kevin Buzzard (Imperial College London): TBA​​

16.12.2020 - Julia Brandes (Chalmers/GU): TBA​​​

Past seminars

24.09.2020 - Jan Gerken (Chalmers/GU): Single-valued maps at genus zero and one

Abstract: The single-valued map for for multiple zeta values (MZVs) due to Francis Brown and Oliver Schnetz is an intriguing algebra homomorphism for MZVs. Surprisingly, it appears in the leading contribution to scattering amplitudes in string theory, relating open- and closed-string amplitudes. Since MZVs are periods of configuration spaces of punctured genus-zero Riemann surfaces, a natural next step is the generalization of the single-valued map to genus-one surfaces. In string theory, these correspond to the subleading contributions to the scattering amplitudes. Using the structures provided by string theory, we propose a genus-one generalization of the single-valued map for MZVs which acts on the level of generating functions of genus-one periods.​

09.09.2020 - Lucile Devin (Chalmers/GU): Chebyshev’s bias and sums of two squares
Abstract: Studying the secondary terms of the Prime Number Theorem in Arithmetic Progressions, Chebyshev claimed that there are more prime numbers congruent to 3 modulo 4 than to 1 modulo 4. We will explain and qualify this claim following the framework of Rubinstein and Sarnak. Then we will see how this framework can be adapted to other questions on the distribution of prime numbers. This will be illustrated by a new Chebyshev-like claim :  there are “more” prime numbers that can be written as a sum of two squares with the even square larger than the odd square than the other way around.

11.06.2020 - Jakob Palmkvist (Chalmers/GU): Tensor hierarchy algebras

Abstract: Tensor hierarchy algebras constitute a new class of non-contragredient Lie superalgebras, whose finite-dimensional members are the simple Lie superalgebras of Cartan type in Kac’s classification. They have proven useful in describing gauge structures in physical models related to string theory. I will review their construction by generators and relations and some of the remarkable features they exhibit.

20.05.2020 - Asbjörn Nordentoft (University of Copenhagen): Reciprocity Laws, Quantum Modular Forms and Additive Twists of Modular L-functions


Abstract:  In an unpublished paper from 2007, Conrey discovered certain ‘reciprocity relations’ satisfied by twisted moments of Dirichlet L-functions, linking the arithmetics of the finite fields F_p, F_q for two different primes p,q (as is the case with quadratic reciprocity). In this talk I will discuss a generalization to twisted moments of twisted modular L-functions. This will lead to a discussion of the notion of quantum modular forms due to Zagier, and in particular we will explain that additive twists of modular L-functions define examples of quantum modular forms. 

06.05.2020 - Martin Raum (Chalmers/GU): Divisibilities of class numbers and partition counts

Abstract: Hurwitz class numbers, class numbers of imaginary quadratic fields, and partition counts are among the most classic quantities in number theory, and for each of them their factorizations, i.e. divisibilities, are celebrated open questions. In the case of class numbers the Cohen-Lehnstra Heuristics provides predictions of of statistical nature. In the case of partition counts, Ramanujan congruences opened the door to a whole new research area in~1920.

We survey recent progress on divisibilities of class numbers and partition counts on arithmetic progressions. These result rely on a two new methods exploiting the finer structure of Fourier coefficients of real-analytic and meromorphic modular forms.

The project on class numbers is partially based on joint work with Olivia Beckwith and Olav Richter. The project on partition counts is partially based on joint work with Olivia Beckwith and Scott Ahlgren.​

04.03.2020 - Jasmin Matz (University of Copenhagen): Distribution of Hecke eigenvalues

Abstract: There are many difficult conjectures about automorphic representations, many of which seem to be out of reach at the moment. It has therefore become increasingly popular to study instead families of automorphic representations and their statistical properties, which allows for additional analytic techniques to be used.

In my talk I want to discuss the distribution of Hecke eigenvalues or, in other words, Satake parameters in the family of spherical unramified automorphic representations of split classical groups.  We obtain an effective distribution of the Satake parameters, when we order the family according to the size of analytic conductor. This has applications to various questions in number theory, for example, low-lying zeros in families of automorphic L-functions, but also yields an effective Weyl law for the underlying locally symmetric space. This is joint work with T. Finis.

26.02.2020 - Kirsti Biggs (Chalmers/GU): Efficient congruencing in ellipsephic sets
 Abstract: An ellipsephic set is a subset of the natural numbers whose elements have digital restrictions in some fixed prime base---for example, the set of positive integers whose digits in the given base are squares. Such sets have a fractal structure and can be viewed as p-adic Cantor sets analogous to those studied over the real numbers. The results of this talk can similarly be viewed from either a number theoretic or a harmonic analytic perspective: we bound the number of ellipsephic solutions to a system of diagonal equations, or, alternatively, we obtain discrete restriction estimates for the moment curve over ellipsephic sets. In this talk, I will outline the key ideas from the proof, which uses Wooley's efficient congruencing method, give motivating examples and highlight the importance of the additive structure of our ellipsephic sets.


12.02.2020 - Kevin Hughes (University of Bristol): Discrete restriction to the curve (x,x^3)

Abstract: In this talk I will motivate the problem of discrete restriction to the curve (x,x^3). This is one of the simplest cases outside the recently introduced and powerful machinery of decoupling and efficient congruencing. While the expected 10th decoupling inequality fails, we show that the nigh-optimal discrete restriction estimate holds. This is work with Trevor Wooley.

19.02.2020 - Nils Matthes (University of Oxford): Motivic periods
Abstract: A period is a complex number which can be written as the integral of an algebraic differential form over a semialgebraic set. This is a classical notion whose roots can be traced back at least to Euler and which conjecturally contains all special values of L-functions of algebraic varieties. Beginning in the 1960s it was realized that the study of periods may be viewed as part of Grothendieck's vision of motives which very recently lead to the notion of "motivic period". Although progress has been made, many fundamental questions about (motivic) periods remain.


05.02.2020 - Pankaj Vishe (Durham University): Rational points on complete intersections over global fields

Abstract: The quantitative arithmetic of the set of rational points on a smooth complete intersection of two quadrics over the function field F_q(t) is obtained, under the assumption that q is odd and n9. The main ingredient here is the development of a Kloosterman refinement over global fields.

28.01.2020 - Jonas Bergström (Stockholm University): Traces of Hecke operators on spaces of Siegel modular forms modulo prime powers

Abstract: I will report on ongoing work, where I apply the Lefschetz fixed point theorem to local systems on the moduli space of abelian varieties of dimension at most 3, and use simple equalities in modular arithmetic, to study traces of Hecke operators on spaces of Siegel modular forms (of degree at most 3) modulo prime powers.

15.01.2020 - Dennis Eriksson (Chalmers/GU): Genus one mirror symmetry

Abstract: Mirror symmetry, in a crude formulation, is usually presented as a correspondence between curve counting on a Calabi--Yau variety X, and some invariants extracted from a mirror family of Calabi--Yau varieties. After the physicists Bershadsky--Cecotti--Ooguri--Vafa (henceforth BCOV), this is organised according to the genus of the curves in X we wish to enumerate, and gives rise to an infinite recurrence of differential equations. In this talk, I will give a general introduction to these problems, and present a rigorous mathematical formulation of the BCOV conjecture at genus one, in terms of a lifting of the Grothendieck--Riemann--Roch. I will explain a proof of the conjecture for Calabi--Yau hypersurfaces in projective space, based on the Riemann--Roch theorem in Arakelov geometry. Our results generalise from dimension 3 to arbitrary dimensions previous work of Fang--Lu--Yoshikawa.
This is joint work with G. Freixas and C. Mourougane.

Published: Thu 24 Sep 2020.