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Monday, 2 October  

Time  Speaker  Title  Location 
15:00  16:00  Dr. Gabriela Estevez Universidade Federal Fluminense 
Abstract
In 1984 Yoccoz proved that any two C^3 orientationpreserving circle homeomorphisms, with the same quantity of nonflat critical points and the same irrational rotation number, are topologically conjugated. For maps with only one critical point, it has been shown that the conjugacy is, in fact, a C^1diffeomorphism. Moreover, in a total Lebesgue measure set of irrational rotation numbers the conjugacy can be improved to be C^{1+\alpha}. In this talk, we will discuss some recent results concerning the smoothness of the conjugacy for maps with more than one critical point, and how these results are obtained using renormalization.
Ergodic theory and dynamical systems seminar
Some recent results on multicritical circle mapsread_more 
Y27H 25 
17:15  18:15  Prof. Dr. Sarah Zerbes 
HG F 30 

17:30  19:00  Prof. Dr. Georg Oberdieck KTH Stockholm 
Abstract
An Enriques surface is the quotient of a K3 surface by a fixed pointfree involution. Klemm and Marino conjectured a formula expressing the GromovWitten invariants of the local Enriques surface in terms of automorphic forms. In particular, the generating series of elliptic curve counts on the Enriques should be the Fourier expansion of (a certain power of) Borcherds automorphic form on the moduli space of Enriques surfaces. In this talk I will explain a proof of this conjecture. The proof uses the geometry of the Enriques CalabiYau threefold in fiber classes. If time permits, I will also discuss various conjectures about nonfiber classes.
Algebraic Geometry and Moduli Seminar
Curve counting on the Enriques surface and the KlemmMarino formularead_more 
Zoom 
Tuesday, 3 October  

Time  Speaker  Title  Location 
10:15  12:00  Johannes Flake MaxPlanckInstitut für Mathematik, Bonn 
HG G 43 

15:05  16:00  Gabriel Arpinocall_made University of Cambridge 
Abstract
我们考虑稀疏线性混合注册的问题ression with two components, where two sparse signals are observed through n unlabelled noisy linear measurements. Prior work has shown that the problem suffers from a significant statisticaltocomputational gap, resembling other computationally challenging highdimensional inference problems such as Sparse PCA and Robust Sparse Mean Estimation. We establish the existence of a more extensive computational barrier for this problem through the method of lowdegree polynomials, but show that the problem is computationally hard only in a very narrow symmetric parameter regime. We identify smooth informationcomputation tradeoffs in this problem and prove that a simple lineartime algorithm succeeds outside of the narrow hard regime. To the best of our knowledge, this is the first thorough study of the interplay between mixture symmetry, signal sparsity, and their joint impact on the computational hardness of mixed sparse linear regression. This is joint work with Ramji Venkataramanan. https://proceedings.mlr.press/v195/arpino23a.html.
DACO Seminar
StatisticalComputational Tradeoffs in Mixed Sparse Linear Regressionread_more 
HG G 19.2 
Wednesday, 4 October  

Time  Speaker  Title  Location 
16:30  17:30  Prof. Dr. Wenjia Jing Tsinghua University 
Abstract
We consider elliptic equations with periodic high contrast coefficients and study the asymptotic analysis when the periodicity is sent to zero and/or the contrast parameters are sent to extreme values. Those coefficients model small inclusions that have very different physical properties compared to the surrounding environment. Homogenization captures the macroscopic effects of those inclusions. We report some quantitative results such as the convergence rates of the homogenization (with proper correctors), uniform regularity for the solutions of the heterogeneous equations, and so on. The talk is based on joint works with Mr. Xin Fu.
Zurich Colloquium in Applied and Computational Mathematics
Quantitative homogenization of elliptic problems in periodic high contrast environmentsread_more 
HG E 1.2 
17:15  18:45  Prof. Dr. Igor Kortchemski ETH Zürich 
Y27H12 
Thursday, 5 October  

Time  Speaker  Title  Location 
15:00  16:00  Andrea Drago 
HG G 19.1 

17:15  18:15  Prof. Dr. Marcus C. Christiansencall_made Universität Oldenburg 
Abstract
What is the probabilistic core of life insurance modelling? What kind of mathematical objects are premiums and reserves? Which modelling assumptions are really necessary and which are not? The presentation will take the audience on a journey through old concepts and modern interpretations. Traditions will be challenged and alternative views presented.
Talks in Financial and Insurance Mathematics
A journey through multistate modelling in life insuranceread_more 
HG G 43 
Friday, 6 October  

Time  Speaker  Title  Location 
10:15  12:00  Johannes Flake MaxPlanckInstitut für Mathematik, Bonn 
HG G 43 

16:00  17:30  Dr. Yalong Cao RIKEN (Japan) 
Abstract
BPS invariants were introduced by GopakumarVafa on CalabiYau 3folds, KlemmPandharipande on CY 4folds and PandharipandeZinger on CY 5folds. They are conjectured to be integers (proven in many cases) and have correspondence with GromovWitten invariants. On holomorphic symplectic 4folds, (ordinary) GW and hence BPS invariants vanish, one can consider reduced GW invariants which are usually nontrivial rational numbers. In this talk, we will introduce BPS invariants for such a reduced theory. Joint works with Georg Oberdieck and Yukinobu Toda.
Algebraic Geometry and Moduli Seminar
GopakumarVafa type invariants of holomorphic symplectic 4foldsread_more 
HG G 43 