Mathematical Institute Calendar

Tuesday, September 26, 2023

13:15-15:00

BBG 119

I will give a leisurely overview of parametrized and highersemiadditivity. In particular I will motivate this concept by giving avariety of examples. As one such example, I will explain how it gives aconceptual interpretation of definitions in (globally) equivariantalgebra and homotopy theory. I will then finish by discussing the closeconnection between generalized semiadditivity and the construction oftransfer maps.

16:00-17:00

HFG 611

In relation to his work on Hilbert'sthird problem, Dehn proved in 1903 that a rectangle can be tiled by squares ifand only if the ratio of its sides is a rational number. In 1994-95Freiling-Rinne and Laczkovich-Szekeres solved a converse problem: for whichreal numbers r can one tile a square by rectangles with side ratio r. Theanswer is much more interesting: the property holds if and only if r is analgebraic number all of whose conjugates have positive real part. Soonafterwards the result was generalised to tilings of arbitrary rectangles byrectangles with a given side ratio. Unfortunately, in this case thecorresponding criterion was somewhat mysterious, and it was not clear whetherit was algorithmically decidable.

Seminar webpage https://utrechtgeometrycentre.nl/ugc-seminar/

In the talk, we give a geometric interpretation of this condition and we showthat it is decidable. Using these methods, we generalise the above results totilings of squares by finitely many rectangles with possibly different sideratios under the extra assumption that all these ratios are algebraic numbers.We also classify all pairs of rectangles which are mutually tileable (there arenontrivial examples!). This is joint work with Radomił Baran.

Seminar webpage https://utrechtgeometrycentre.nl/ugc-seminar/

Thursday, September 28, 2023

09:15-10:15

BBG - 223

Abstract: (coming soon) (joint work with J. Commelin and P. Habbegger)

AG seminar webpage: https://webspace.science.uu.nl/~marse004/ag_seminar.html

Friday, October 6, 2023

14:00-17:00

Ruppert 042

Dutch Differential Topology and Geometry seminar

Inbar Klang - Manifold topology via isovariant homotopy

see description

Homotopy theory has proven to be a robust tool for studying non-homotopical questions about manifolds; for example, surgery theory addresses manifold classification questions using homotopy theory. In joint work with Sarah Yeakel, we are developing a program to study manifold topology via isovariant homotopy theory. I'll explain what isovariant homotopy theory is and how it relates to the study of manifolds via their configuration spaces, and talk about an application to fixed point theory.

Website of the DDTG seminar: https://www.few.vu.nl/~trt800/ddtg.html

Website of the DDTG seminar: https://www.few.vu.nl/~trt800/ddtg.html

Tuesday, October 10, 2023

14:00-16:00

Vrije Universiteit Amsterdam NU Building 9A46

16:00-17:00

HFG - 611

UGC seminar talk

Leo Tzou (UvA) - Probing the World with Waves - From the Subatomic to the Cosmos

see description

In this talk we look at mathematical questions which arise naturally from imaging things that are invisible to the naked eye, ranging from models inspired by quantum mechanics to astronomy. We will explore how such inverse problems bridge different mathematical disciplines such as partial differential equations, geometry, and dynamical systems while simultaneously connecting these classical mathematical fields to modern topics in data science.

Seminar webpage: https://utrechtgeometrycentre.nl/ugc-seminar/

Seminar webpage: https://utrechtgeometrycentre.nl/ugc-seminar/

Wednesday, October 11, 2023

Thursday, October 12, 2023

16:00-17:00

KBG Pangea

Kan Lectures

Mikhail Kapranov - Adjoint functors, continued fractions and categorified perverse sheaves I

see description

There will be:

Remarkably, some algebraic aspects of CF find their analogs in the very

foundations of category theory: in relation to the concept of adjoint functors

introduced by D. Kan in 1958. More precisely, Euler's continuants (the universal

polynomials expressing the numerators and denominators of convergents of

a CF) lift to certain complexes built out of a given functor and its iterated

adjoints. Requiring exactness of some of these complexes leads to the

concept of an N-spherical functor which encompasses ordinary spherical functors

for N=4. Such functors describe N-periodic semi-orthogonal decompositions

of (enhanced) triangulated categories.

The lectures will present the classical continuant formalism, its categorical lifting

and the point of view on spherical and N-spherical functors as regular and irregular

perverse schobers (categorified perverse sheaves) on the complex plane. They

are based on joint work with T. Dyckerhoff, V. Schechtman and Y. Soibelman.

Friday, October 13, 2023

14:30-15:30

KBG Pangea

16:00-17:00

KBG Pangea

Tuesday, October 24, 2023

Tuesday, October 31, 2023

16:00-17:00

HFG 611

Zeros of the Riemann zeta function and eigenvalues of quantized chaotic Hamiltonians appears to have something in common. Namely, they both seem to be ruled by random matrix theory and consequently should exhibit "repulsion" in the sense that small gaps between elements are very rare. More mysteriously, while zeros of different L-functions (i.e., generalizations of the Riemann zeta function) are "mostly independent" they also exhibit subtle repulsion effects on zeros of other L-functions.

We will give a survey of the above phenomena. Time permitting we will also discuss repulsion between eigenvalues of "arithmetic Seba billiards", a certain singular perturbation of the Laplacian on the 3D torus R^3/Z^3. The perturbation is weak enough to allow for arithmetic features from the unperturbed system to be brought into play, yet strong enough to provably induce repulsion.

Seminar webpage https://utrechtgeometrycentre.nl/ugc-seminar/

We will give a survey of the above phenomena. Time permitting we will also discuss repulsion between eigenvalues of "arithmetic Seba billiards", a certain singular perturbation of the Laplacian on the 3D torus R^3/Z^3. The perturbation is weak enough to allow for arithmetic features from the unperturbed system to be brought into play, yet strong enough to provably induce repulsion.

Seminar webpage https://utrechtgeometrycentre.nl/ugc-seminar/

Tuesday, November 7, 2023

16:00-17:00

HFG-611

Tuesday, November 21, 2023

16:00-17:00

HFG-611

Wednesday, November 29, 2023

Tuesday, December 5, 2023

16:00-17:00

HFG 611

Thursday, December 14, 2023

Tuesday, December 19, 2023