London Number Theory Seminar 



The London Number Theory Seminar is held weekly, on Wednesdays, during term time. The location of the seminar cycles between KCL, Imperial College and UCL.
This term (Spring 2017), the seminar will be hosted by UCL, and will be on Wednesdays at 4:30pm5:30pm (note nonstandard time) in UCL in Malet Place Engineering, Room 1.02 (except on February 15 and 22, when it will be in Archaeology, Room G6) (note nonstandard place), starting on 11th January and finishing on March 22nd. The seminar is organised by Sarah Zerbes. The only hint I have for finding the seminar this term is this generic map link for UCL. Good luck.
The seminar will be preceded by tea and biscuits at 4pm in room 606.
The most uptodate list of speakers/titles is at Sarah Zerbes' website here. The last time I looked it said this:
11/01/17 Chris Skinner (Princeton)
Title: Recent progress on the Iwasawa theory of elliptic curves and modular forms.
Abstract: This talk will describe some of the recent work on the Iwasawa theory of modular forms (at both ordinary and nonordinary primes) with an emphasize on the strategy of proof, which involves two different main conjectures.
18/01/17 Jack Lamplugh (UCL)
Title: An Euler system for a pair of CM modular forms.
Abstract: Given a pair of modular forms and a prime p, LeiLoefflerZerbes have constructed an Euler system for the tensor product of the padic Galois representations attached to each of the forms. When the forms have CM by distinct imaginary quadratic fields, this representation is induced from a character $\chi$ over an imaginary biquadratic field F. I will explain how one can use this Euler system to obtain upper bounds for Selmer groups associated to $\chi$ over the $\mathbf{Z}_p^3$extension of F.
25/01/17 Rachel Newton (Reading University)
Title: The Hasse norm principle for abelian extensions
Abstract: Let $L/K$ be an extension of number fields and let $J_L$ and $J_K$ be the associated groups of ideles. Using the diagonal embedding, we view $L^\times$ and $K^\times$ as subgroups of $J_L$ and $J_K$ respectively. The norm map $N: J_L\to J_K$ restricts to the usual field norm $N: L^\times\to K^\times$ on $L^\times$. Thus, if an element of $K^\times$ is a norm from $L^\times$, then it is a norm from $J_L$. We say that the Hasse norm principle holds for $L/K$ if the converse holds, i.e. if every element of $K^\times$ which is a norm from $J_L$ is in fact a norm from $L^\times$. The original Hasse norm theorem states that the Hasse norm principle holds for cyclic extensions. Biquadratic extensions give the smallest examples for which the Hasse norm principle can fail. One might ask, what proportion of biquadratic extensions of $K$ fail the Hasse norm principle? More generally, for an abelian group $G$, what proportion of extensions of $K$ with Galois group $G$ fail the Hasse norm principle? I will describe the finite abelian groups for which this proportion is positive. This involves counting abelian extensions of bounded discriminant with infinitely many local conditions imposed, which is achieved using tools from harmonic analysis. This is joint work with Christopher Frei and Daniel Loughran.
1/2/17 Atsuhira Nagano (KCL/Waseda University)
Title: K3 surfaces and a construction of a Shimura variety
Abstract: In old times, elliptic modular functions appeared in the study of elliptic curves. They are applied to the construction of class fields. (This is classically called Kronecker's Jugendtraum.) K3 surfaces are 2dimensional analogy of elliptic curves. In this talk, the speaker will present an extension of the classical result by using K3 surfaces. Namely, we will obtain Hilbert modular functions via the periods of K3 surfaces and construct a certain model of a Shimura variety explicitly.
8/2/17 Christian Johansson (University of Cambridge)
Title: TBA
15/2/17 (note room change: Archaeology, Room G6)
Alan Lauder (Oxford)
Title: TBA
22/2/17 (note room change: Archaeology, Room G6)
Erick Knight (Harvard/Bonn)
Title: A padic JacquetLanglands correspondence
Abstract: In this talk, I will construct a padic JacquetLanglands correspondence, which is a correspondence between Banach space representations of GL2(Qp) and Banach space representations of the unit group of the quaternion algebra D over Qp. The correspondence satisfies localglobal compatibility with the completed cohomology of Shimura curves, as well as a compatibility with the classical JacquetLanglands correspondence, in the sense that the $D^\times$ representations can often be shown to have the expected locally algebraic vectors.
1/3/17 Giuseppe Ancona (UniversitĂ© de Strasbourg)
Title: Standard conjectures for abelian fourfolds
Abstract: Let X be a smooth projective variety and V be the finite dimensional Q vector space of algebraic cycles on X modulo numerical equivalence. Grothendieck defined a quadratic form on V (basically using the intersection product) and conjectured that it is positive definite. This conjecture is a formal consequence of Hodge Theory in characteristic zero, but almost nothing is known in positive characteristic. Instead of studying this quadratic form at the non archimedean place (the signature) we will study it at the padic places. It turns out that this question is more treatable. Moreover, using a product formula formula, the padic information will give us non trivial informations on the non archimedean place. For instance we will show the original conjecture when X is an abelian variety of dimension 4.
8/3/17 CĂ©line Maistret (University of Warwick)
Title: TBA
15/3/17 Jorge Urroz (UPC)
Title: TBA
22/3/17 Otto Overkamp (Imperial)
Title: TBA
The seminar will be preceded by the Study Groups, and this term there are two of them, one on padic integration running 13001415 and one on padic Hodge theory running 14301600.
A list of previous seminar talks is here.
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This page is maintained by Kevin Buzzard.