BEGIN:VCALENDAR
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PRODID:researchseminars.org
CALSCALE:GREGORIAN
X-WR-CALNAME:researchseminars.org
BEGIN:VEVENT
SUMMARY:Adam Logan (Carleton University and Tutte Institute)
DTSTART:20200622T140000Z
DTEND:20200622T150000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/1
DESCRIPTION:Title: Explicit coverings of K3 surfaces by squares of curves\nby Adam
Logan (Carleton University and Tutte Institute) as part of Leiden Algebra\
, Geometry\, and Number Theory Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/1/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Rachel Newton (University of Reading)
DTSTART:20200629T140000Z
DTEND:20200629T150000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/2
DESCRIPTION:Title: Explicit uniform bounds for Brauer groups of singular K3 surfaces\nby Rachel Newton (University of Reading) as part of Leiden Algebra\, Ge
ometry\, and Number Theory Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/2/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Matteo Verzobio (Università di Pisa)
DTSTART:20201204T150000Z
DTEND:20201204T160000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/3
DESCRIPTION:Title: Sequences associated to elliptic curves\nby Matteo Verzobio (Uni
versità di Pisa) as part of Leiden Algebra\, Geometry\, and Number Theory
Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/3/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Raymond van Bommel (MIT)
DTSTART:20201211T150000Z
DTEND:20201211T160000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/4
DESCRIPTION:Title: Computation of BSD invariants in higher genus\nby Raymond van Bo
mmel (MIT) as part of Leiden Algebra\, Geometry\, and Number Theory Semina
r\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/4/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Lawrence Barrott (Boston College)
DTSTART:20210222T150000Z
DTEND:20210222T160000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/5
DESCRIPTION:Title: Counting tangent curves via degenerations\nby Lawrence Barrott (
Boston College) as part of Leiden Algebra\, Geometry\, and Number Theory S
eminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/5/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jan Vonk (Universiteit Leiden)
DTSTART:20210301T150000Z
DTEND:20210301T160000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/6
DESCRIPTION:Title: Quadratic Chabauty and modular curves\nby Jan Vonk (Universiteit
Leiden) as part of Leiden Algebra\, Geometry\, and Number Theory Seminar\
n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/6/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Jana Sotáková (UvA/QuSoft)
DTSTART:20210315T150000Z
DTEND:20210315T160000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/7
DESCRIPTION:Title: Bruhat-Tits trees and supersingular elliptic curves\nby Jana Sot
áková (UvA/QuSoft) as part of Leiden Algebra\, Geometry\, and Number The
ory Seminar\n\n\nAbstract\nCryptographic schemes based on computing isogen
ies of supersingular elliptic curves are a fairly young topic in post-quan
tum cryptography. Their main benefits are their size: public keys are just
a few field elements. Their main drawbacks are their speed - and underlyi
ng algebraic structure\, which has not been explored fully. We will focus
on the SIDH family of proposals and propose studying them from the view of
Bruhat-Tits trees. These trees are simple combinatorial objects\, we can
describe them using 2x2 matrices\, and use them to capture the information
on torsion points coming from SIDH. This is joint work with Laia Amorós\
, Annamaria Iezzi\, Kristin Lauter\, and Chloe Martindale.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/7/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Carlo Pagano (University of Glasgow/MPIM Bonn)
DTSTART:20210322T150000Z
DTEND:20210322T160000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/8
DESCRIPTION:Title: On the negative Pell equation\nby Carlo Pagano (University of Gl
asgow/MPIM Bonn) as part of Leiden Algebra\, Geometry\, and Number Theory
Seminar\n\n\nAbstract\nHow often does the ring of integers of a real quadr
atic field have a unit with norm -1? In 1995 Peter Stevenhagen proposed a
precise conjectural asymptotic formula describing how many such real quadr
atic fields should be out there when counted by discriminant. I will discu
ss a joint upcoming work with Peter Koymans where we establish Stevenhagen
's conjecture.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/8/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Owen Biesel (Carleton College)
DTSTART:20210503T140000Z
DTEND:20210503T150000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/9
DESCRIPTION:Title: A norm functor for quadratic algebras\nby Owen Biesel (Carleton
College) as part of Leiden Algebra\, Geometry\, and Number Theory Seminar\
n\n\nAbstract\nThe trace and norm maps from Galois theory are two members
of a menagerie of various norm functors for different types of algebraic d
ata: given a ring R with a finite locally-free algebra A (both commutative
and unital)\, we can take the trace or norm of an element of A to get an
element of R\, we can take the "norm" of a line bundle over A to get a lin
e bundle over R\, and thanks to Ferrand we can even take an arbitrary A-mo
dule and construct its "norm" as an R-module. In this talk we construct a
norm functor for the data of a quadratic algebra: given a locally-free ran
k-2 A-algebra D\, we produce a locally-free rank-2 R-algebra Nm(D) in a wa
y that is compatible with other norm functors and which extends a known co
nstruction for étale quadratic algebras. We also conjecture a relationshi
p between discriminant algebras and this new norm functor.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/9/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Mirko Mauri (MPIM Bonn)
DTSTART:20210329T140000Z
DTEND:20210329T150000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/10
DESCRIPTION:Title: Intersection cohomology of character varieties of rank two\nby
Mirko Mauri (MPIM Bonn) as part of Leiden Algebra\, Geometry\, and Number
Theory Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/10/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Giulio Orecchia (EPFL)
DTSTART:20210419T140000Z
DTEND:20210419T150000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/11
DESCRIPTION:Title: Beschrijving: Title: From algebra to topology: the fundamental grou
p via Frobenius\nby Giulio Orecchia (EPFL) as part of Leiden Algebra\,
Geometry\, and Number Theory Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/11/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Rosa Schwarz (Universiteit Leiden)
DTSTART:20210531T140000Z
DTEND:20210531T150000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/12
DESCRIPTION:Title: The double-double ramification cycle\nby Rosa Schwarz (Universi
teit Leiden) as part of Leiden Algebra\, Geometry\, and Number Theory Semi
nar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/12/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Xavier Caruso (CNRS/Université de Bordeaux)
DTSTART:20210614T140000Z
DTEND:20210614T150000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/13
DESCRIPTION:Title: Fast evaluation of some p-adic special functions\nby Xavier Car
uso (CNRS/Université de Bordeaux) as part of Leiden Algebra\, Geometry\,
and Number Theory Seminar\n\n\nAbstract\nIn this talk\, I will present fas
t algorithms for computing values of p-adic functions which are solutions
of a small linear differential equation. This includes in particular expon
entials\, polylogarithms\, hypergeometric functions and many special funct
ions appearing in the cohomology of p-adic fibrations.\nAs an application\
, building upon previous works by Asakura and Kedlaya\, I will derive an a
lgorithm for computing special values of the Dwork hypergeometric function
with quasi-linear runtime with respect to the target precision.\nJoint wo
rk with Marc Mezzarobba\, Nobuki Takayama and Tristan Vaccon.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/13/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Elie Eid (Université de Rennes 1)
DTSTART:20210628T140000Z
DTEND:20210628T150000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/15
DESCRIPTION:Title: Computing Cantor division polynomials via differential equations\nby Elie Eid (Université de Rennes 1) as part of Leiden Algebra\, Geome
try\, and Number Theory Seminar\n\n\nAbstract\nThe computation of Cantor d
ivision polynomials is an essential step in Pila's algorithm for counting
points on hyperelliptic curves and their Jacobians over finite fields. Cla
ssical algorithms for computing these polynomials are usually based on Can
tor’s recurrence formulas and Cantor’s algorithm for adding points on
Jacobians. Although\, they exhibit acceptable running time in practice\, t
heir theoretical complexity has not been well studied yet and experiments
show that they become much slower when the degree or the genus get higher.
\nIn this talk\, I will provide an efficient way to calculate them\, based
on solving some non-linear differential equations.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/15/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Evis Ieronymou (University of Cyprus)
DTSTART:20211115T151500Z
DTEND:20211115T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/16
DESCRIPTION:Title: Brauer-Manin obstruction and zero-cycles on surfaces\nby Evis I
eronymou (University of Cyprus) as part of Leiden Algebra\, Geometry\, and
Number Theory Seminar\n\n\nAbstract\nWe give an introduction on the Braue
r-Manin obstruction to the Hasse principle and present some recent results
on zero-cycles on surfaces.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/16/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Rachel Newton (King's College London)
DTSTART:20211117T151500Z
DTEND:20211117T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/17
DESCRIPTION:Title: Arithmetic of rational points and zero-cycles on Kummer varieties\nby Rachel Newton (King's College London) as part of Leiden Algebra\, G
eometry\, and Number Theory Seminar\n\n\nAbstract\nIn 1970\, Manin observe
d that the Brauer group Br(X) of a variety X over a number field K can obs
truct the Hasse principle on X. In other words\, the lack of a K-point on
X despite the existence of points over every completion of K is sometimes
explained by non-trivial elements in Br(X). This so-called Brauer-Manin ob
struction may not always suffice to explain the failure of the Hasse princ
iple but it is known to be sufficient for some classes of varieties (e.g.
torsors under connected algebraic groups) and conjectured to be sufficient
for rationally connected varieties and K3 surfaces.\nA zero-cycle on X is
a formal sum of closed points of X. A rational point of X over K is a zer
o-cycle of degree 1. It is interesting to study the zero-cycles of degree
1 on X\, as a generalisation of the rational points. Yongqi Liang has show
n that for rationally connected varieties\, sufficiency of the Brauer-Mani
n obstruction to the Hasse principle for rational points over all finite e
xtensions of K implies sufficiency of the Brauer-Manin obstruction to the
Hasse principle for zero-cycles of degree 1 over K. In this talk\, I will
discuss joint work with Francesca Balestrieri where we extend Liang's resu
lt to Kummer varieties.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/17/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Leo Herr (University of Utah)
DTSTART:20211122T151500Z
DTEND:20211122T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/18
DESCRIPTION:by Leo Herr (University of Utah) as part of Leiden Algebra\, G
eometry\, and Number Theory Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/18/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Emre Sertöz (Leibniz Universität Hannover)
DTSTART:20211201T151500Z
DTEND:20211201T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/19
DESCRIPTION:Title: Separating periods of quartic surfaces\nby Emre Sertöz (Leibni
z Universität Hannover) as part of Leiden Algebra\, Geometry\, and Number
Theory Seminar\n\n\nAbstract\nWe give an effective lower bound on the dis
tance between two distinct periods of a given quartic surface defined over
the algebraic numbers. The main ingredient is the determination of height
bounds on components of the Noether--Lefschetz loci. This makes it possib
le to study the Diophantine properties of periods of quartic surfaces and
to certify a part of the numerical computation of their Picard groups. Thi
s is joint work with Pierre Lairez.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/19/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Sergej Monavari (Universiteit Utrecht)
DTSTART:20211208T151500Z
DTEND:20211208T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/20
DESCRIPTION:Title: Higher rank K-theoretic Donaldson-Thomas Theory of points\nby S
ergej Monavari (Universiteit Utrecht) as part of Leiden Algebra\, Geometry
\, and Number Theory Seminar\n\n\nAbstract\nA classical way to produce inv
ariants is through intersection theory\, usually on a smooth projective va
riety. We give a gentle introduction on how to use torus actions to refine
invariants in several directions\, for example K-theoretic and virtual in
variants. As a concrete example\, we explain how to extract meaningful inv
ariants from the Quot schemes of quasi-projective smooth toric threefolds
and how to refine them. We present and prove various closed formulas for d
ifferent flavours of higher rank Donaldson-Thomas invariants of points\, s
olving a series of conjectures proposed in String Theory. This is based on
joint work with N. Fasola and A. Ricolfi.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/20/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Priyanka Majumder (Darmstadt)
DTSTART:20220209T151500Z
DTEND:20220209T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/21
DESCRIPTION:Title: Bounds for canonical Green’s functions of Fuchsian subgroups of P
SL2(R)\nby Priyanka Majumder (Darmstadt) as part of Leiden Algebra\, G
eometry\, and Number Theory Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/21/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Shengyuan Huang (Birmingham)
DTSTART:20220221T151500Z
DTEND:20220221T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/22
DESCRIPTION:Title: Lie structures in derived categories\nby Shengyuan Huang (Birmi
ngham) as part of Leiden Algebra\, Geometry\, and Number Theory Seminar\n\
n\nAbstract\nFor a closed embedding $X\\hookrightarrow S$ of smooth scheme
s with a first order splitting\, the derived self-intersection $X\\times^R
_SX$ and the shifted normal bundle $N_{X/S}[-1]$ carry Lie structures. In
this talk\, we discuss an analogue of the exponential map from a Lie algeb
ra to the corresponding Lie group in this setting and its application in t
he study of orbifold Hochschild cohomology product.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/22/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Giacomo Mezzedimi (Hannover)
DTSTART:20220228T151500Z
DTEND:20220228T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/23
DESCRIPTION:Title: Projective models of Enriques surfaces via elliptic curves\nby
Giacomo Mezzedimi (Hannover) as part of Leiden Algebra\, Geometry\, and Nu
mber Theory Seminar\n\n\nAbstract\nEnriques surfaces form one of the four
classes of algebraic surfaces of Kodaira dimension zero in the Enriques-Ko
daira classification. The first examples of Enriques surfaces were constru
cted by Enriques as minimal desingularizations of certain non-normal sexti
cs in P^3\, which are now called Enriques sextics. The goal of this talk w
ill be to show that every Enriques surface over an algebraically closed fi
eld of characteristic different from 2 can be realized as the minimal desi
ngularization of an Enriques sextic. I will introduce the main tool used i
n the proof\, namely isotropic sequences\, and I will show how the presenc
e of many elliptic fibrations on the surface leads to "good" projective mo
dels. I will then discuss some geometric implications of the result and so
me relevant examples. This is joint work in progress with Gebhard Martin a
nd Davide Veniani.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/23/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Tommy Hofmann (Siegen)
DTSTART:20220307T151500Z
DTEND:20220307T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/24
DESCRIPTION:Title: Lattice isomorphism and the integral matrix similarity problem\
nby Tommy Hofmann (Siegen) as part of Leiden Algebra\, Geometry\, and Numb
er Theory Seminar\n\n\nAbstract\nDeciding whether two lattices over orders
of finite-dimensional algebras over number fields is a classical problem
in algorithmic number theory. We present a new algorithm for this problem\
, assuming that the Wedderburn decomposition of the algebra behaves nice.
As an application we discuss the connection to the similarity problem for
integral matrices (the conjugacy problem in GL(n\, Z)).\nThe resulting alg
orithm for the latter problem is the first with proven complexity and perf
orms very well in practice. This is joint work with Werner Bley and Henri
Johnston.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/24/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Vova Soslino (St. Petersburg/Regensburg)
DTSTART:20220315T111500Z
DTEND:20220315T121500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/25
DESCRIPTION:Title: Weight structures and applications I: structural results\nby Vo
va Soslino (St. Petersburg/Regensburg) as part of Leiden Algebra\, Geometr
y\, and Number Theory Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/25/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Elden Elmanto (Harvard)
DTSTART:20220316T151500Z
DTEND:20220316T161500Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/26
DESCRIPTION:Title: Weight structures and applications II: affine stacks and noncommuta
tive Hodge theory\nby Elden Elmanto (Harvard) as part of Leiden Algebr
a\, Geometry\, and Number Theory Seminar\n\nAbstract: TBA\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/26/
END:VEVENT
BEGIN:VEVENT
SUMMARY:Libby Taylor (Stanford)
DTSTART:20220425T170000Z
DTEND:20220425T180000Z
DTSTAMP:20260404T095654Z
UID:LAGeNT/27
DESCRIPTION:Title: Higher Brauer groups and higher Azumaya algebras\nby Libby Tayl
or (Stanford) as part of Leiden Algebra\, Geometry\, and Number Theory Sem
inar\n\n\nAbstract\nLet X be some scheme. We are all familiar with the fa
ct that classes in H^1(X\,G_m) correspond to line bundles\, or invertible
sheaves. Most of us have also seen the interpretation of H^2(X\,G_m) as A
zumaya algebras\, which are invertible bundles up to Morita equivalence.
This raises the question: what about H^3\, or H^4\, or H^n? Can they be i
nterpreted as some kind of invertible objects over X? For H^3\, the answe
r turns out to be yes\, and we will describe objects we call 2-Azumaya alg
ebras which provide such an interpretation.\n
LOCATION:https://stable.researchseminars.org/talk/LAGeNT/27/
END:VEVENT
END:VCALENDAR