The Algebra and Number Theory group of the University of Luxembourg hosts three seminars.

- The
**Luxembourg Number Theory Seminar**hosts invited speakers and takes place occasionally; the seminar will partly be held online. - In the
**Research Seminar**the group members study a topic together; during term time the seminar takes place weekly. - In the
**Work in Progress Seminar**the group discusses its work in progress; during term time the seminar takes place weekly.

Everyone is invited to attend! For more information, please contact Alexandre Maksoud, Andrea Conti or Gabor Wiese.

Date (Room) | Speaker | Title |

13/10/2020, 14:00 (MSA 3.220) | Gautier Ponsinet (Max Planck Institute for Mathematics) | Universal norms of p-adic Galois representations and the Fargues-Fontaine curve |

27/10/2020, 15:00 (online) | Paul Pollack (University of Georgia) | Thoughts on the order of a mod p |

03/11/2020, 14:00 (online) | Nikita Karpenko (University of Alberta) | An ultimate proof of Hoffmann-Totaro's conjecture |

01/12/2020, 14:00 (online) | Ariel Weiss (Einstein Institute of Mathematics) | TBA |

14/12/2020, all day (online) | Luxembourg Number Theory Day 2020 |

Date (Room) | Speaker | Title |

29/09/2020, 14:00 (MSA 3.100) | Alexandre Maksoud | On Iwasawa theory and Bloch-Kato conjecture for Artin motives |

06/10/2020, 13:30 (MSA 3.220) | Daniel Berhanu Mamo | Eisenstein series and newform theory |

20/10/2020, 14:00 (MSA 3.220) | Arturo Jaramillo/Xiaochuan Yang | Selberg's theorem via Stein's method |

27/10/2020, 13:45 (online) | Sebastiano Tronto | Kummer theory for algebraic groups |

10/11/2020, 14:00 (online) | Arturo Jaramillo | A new probabilistic approach to Erdos-Kac theorem |

17/11/2020, 14:00 (online) | Andrea Conti | Trianguline representations and functoriality |

24/11/2020, 14:00 (online) | Flavio Perissinotto | Kummer theory for products of 1-dimensional tori |

08/12/2020, 14:00 (online) | Pietro Sgobba | tba |

You can find here a tentative schedule.

Date (Room) | Speaker | Title |

29/09/2020, 10:30 (MSA 3.100) | Andrea Conti | Introduction |

06/10/2020, 10:30 (MSA 3.220) | Bryan Advocaat | Valuations |

13/10/2020, 10:30 (MSA 3.220) | Alexandre Maksoud | Spectral and sober spaces |

20/10/2020, 10:30 (MSA 3.220) | Daniel Berhanu Mamo | Valuation spectra |

27/10/2020, 10:30 (online) | Alexandre Maksoud | Non-archimedean rings |

03/11/2020, 10:30 (online) | Emiliano Torti | f-adic rings and Tate rings |

10/11/2020, 10:30 (online) | Andrea Conti | Adic spectra of affinoid rings, I |

17/11/2020, 10:30 (online) | Bryan Advocaat | Adic spectra of affinoid rings, II |

24/11/2020, 10:30 (online) | ? | Adic spaces, I |

01/12/2020, 10:30 (online) | ? | Adic spaces, II |

08/12/2020, 10:30 (online) | ? | From rigid analytic spaces and formal schemes to adic spaces |

**Alexandre Maksoud (uni.lu)*** On Iwasawa theory and Bloch-Kato conjecture for Artin motives *

Inspired by the works of Perrin-Riou and of Benois we formulate a new cyclotomic Iwasawa Main Conjecture (IMC) for Artin motives, as well as an Exceptional Zeros Conjecture in this context. When the Artin representation is monomial, we show that our conjectures follow from the higher rank cyclotomic IMC recently introduced by Burns, Kurihara and Sano, together with the Iwasawa-theoretic Mazur-Rubin-Sano conjecture. We highlight some potential applications to a better understanding of special values of Artin L-functions at $s=0$, and to a conjecture on iterated p-adic integrals of Darmon-Lauder-Rotger.

**Daniel Berhanu Mamo (uni.lu)*** Eisenstein series and newform theory *

We set up a variant of strong multiplicity one theorems for Katz modular forms which admit a reducible mod $p$ Galois representation. An example that illustrates the main theorem will be presented.

**Gautier Ponsinet*** Universal norms of $p$-adic Galois representations and the Fargues-Fontaine curve*

In 1996, Coates and Greenberg computed explicitly the module of universal norms for abelian varieties in perfectoid field extensions. The computation of this module is essential to Iwasawa theory, notably to prove "control theorems" for Selmer groups generalising Mazur's foundational work on the Iwasawa theory of abelian varieties over $\mathbb{Z}_p$-extensions. Coates and Greenberg then raised the natural question on possible generalisations of their result to general motives. In this talk, I will present a new approach to this question relying on the classification of vector bundles over the Fargues-Fontaine curve, which enables to answer Coates and Greenberg's question affirmatively in new cases.

**Arturo Jaramillo and Xiaochuan Yang (uni.lu)*** Selberg's theorem via Stein's method *

Click here for the abstract.

**Sebastiano Tronto*** Kummer theory for algebraic groups*

If G is a commutative and connected algebraic group over a number field K and A is a finitely generated and torsion-free subgroup of G(K), we can consider the set n^{-1}A={P in G(Kbar) | nP in A} of n-division points of A in an algebraic closure Kbar of K, for any positive integer n. The field extension K(n^{-1}A) of K generated by these points is Galois and it contains the n-torsion field K(G[n]) of G; we are interested in studying, among other things, its degree over this torsion field. This kind of extensions have been studied for example by Ribet [1], but the methods found in the literature are usually non-effective. In this talk I will present recent effective results of myself and Lombardo in the case of non-CM elliptic curves [2]. I will also outline a general framework, developped in [3], to reduce the study of these extensions to that of some arithmetic properties of A and certain properties of the Galois representations attached to G.

[1] Kennet A. Ribet, Kummer theory on extensions of abelian varieties by tori, Duke Mathematical Journal, 1979.

[2] Davide Lombardo and S. T., Explicit Kummer theory for elliptic curves, ArXiv preprint, 2019.

[3] S. T., Radical entanglement for elliptic curves, ArXiv preprint, 2020.

**Paul Pollack (University of Georgia)*** Thoughts on the order of a mod p*

I will discuss some old problems concerning the distribution of the orders of a modulo p, for a fixed integer a and varying primes p. The emphasis will be on connections between these problems and recent work of the speaker with K. Agrawal (UGA) --- on finite sets of integers at least one of which usually has a large order mod p --- and Z. Engberg (Wasatch Academy, UT) --- on arithmetic properties of Mersenne numbers.

**Nikita Karpenko (University of Alberta)*** An ultimate proof of Hoffmann-Totaro's conjecture*

We prove the last open case of the conjecture on the possible values of the first isotropy index of an anisotropic quadratic form over a field. It was initially stated by Detlev Hoffmann for fields of characteristic not 2 and then extended to arbitrary characteristic by Burt Totaro. The initial statement was proven by the speaker in 2002. In characteristic 2, the case of a totally singular quadratic form was done by Stephen Scully in 2015 and the nonsingular case by Eric Primozic in early 2019.

**Andrea Conti (uni.lu)*** Trianguline representations and functoriality*

I will introduce the notion of triangulinity for a p-adic representation of the absolute Galois group of a p-adic field, explaining how having this property at p is linked to modularity for a global Galois representation. As an application of this theory, I will present some known results and work in progress on how to prove that an n-dimensional global Galois representation is modular if and only if it is modular after composition with an algebraic representation of GL_n of dimension at least 2.

**Flavio Perissinotto (uni.lu)*** Kummer theory for porducts of 1-dimensional tori*

Classical Kummer theory concerns the study of cyclotomic-Kummer extensions, which can be interpreted as torsion and division fields for the multiplicative group. It is natural to address the same problems for general 1-dimensional tori and for products of 1-dimensional tori. In this talk I will explain how to compute the degree of division fields for products of 1-dimensional tori defined over a number field. The strategy is reducing first to a single 1-dimensional torus and then to the case of the multiplicative group, which amounts to understanding whether the splitting field of the torus is contained or not in the given division field.

Last modification: 19 November 2020.