Tidligere arrangementer - Side 105

Modular forms are certain complex-analytic functions on the upper-half plane. They can also be interpreted as giving linear-algebraic invariants of elliptic curves, perhaps equipped with some extra structure, and in this way they reveal their algebraic-geometric nature. One of the most fundamental modular forms is the Dedekind eta function. However, it seems that only recently has it been pinned down precisely what extra structure on an elliptic curve is needed to define eta. Namely, Deligne was able to express this extra structure in terms of the 2- and 3-power torsion of the elliptic curve. Deligne's proof, apparently, is computational. In this talk I'll describe a conjectural reinterpretation of Deligne's result, together with some supporting results and a hint at a possible conceptual proof. The reinterpretation is homotopy theoretic, the key being to think of an elliptic curve as giving a class in framed cobordism. This directly connects the number "24" which often appears in the study of eta to the 3rd stable stem in topology. 

Friday seminar by Arnaud Le Rouzic. NEW TIME: 12.15

P?l Kristian Eriksen - Institutt for lingvistiske og nordiske studier, UiO

Johannes Kleppe, H?gskolen i Buskerud og Vestfold, gives the Seminar in Algebra and Algebraic Geometry:

Abelian varieties XII

Partnerforums fjerde nettverksm?te om arbeids- og  organisasjonsformer handler om hvordan arbeidsprosesser kan fremme kunnskapsdeling og effektiv bruk av medarbeidernes kompetanse.

Hans Olav Melberg, Associate Professor - Department of Health Management and Health Economics, UiO

I will discuss joint work in progress with David Gepner, computing the ring of endomorphisms of the equivariant motivic sphere spectrum, for a finite group. The result is a combination of the endomorphism ring of the equivariant topological sphere spectrum (which equals the Burnside ring by a result of Segal) and that of the motivic sphere spectrum (which equals the Grothendieck-Witt ring of quadratic forms by a result of Morel). This computation is a corollary of a tom Dieck style splitting for certain equivariant motivic homotopy groups.   

Martijn Caspers (M¨¹nster) will give a talk with title: The Haagerup property for arbitrary von Neumann algebras

Abstract: The Haagerup property is an approximation property for both groups and operator algebras that has important applications in for example the Baum-Connes conjecture or von Neumann algebra theory. In this talk we show that the Haagerup property is an intrinsic invariant of an arbitrary von Neumann algebra. We also discuss stability properties of the Haagerup property under constructions as free products, graph products and crossed products. Finally we discuss alternative characterizations in terms of the existence of suitable quadratic forms.

Jan Fredrik Bj?rnstad (Statistics Norway and Dept. of Math.,UiO) gives a seminar in room 107, 1st floor N.H. Abels House at 14:15 November 18th: Survey sampling the way I see it.

This is a work we had done jointly with Garkusha (after Voevodsky) arXiv:1409.4372. Using the machinery of framed sheaves developed by Voevodsky, a triangulated category of framed motives is introduced and studied. To any smooth algebraic variety X in Sm/k, the framed motive M_fr(X) is associated in that category . Also, for any smooth scheme X in Sm/k an explicit quasi-fibrant motivic replacement of its suspension P1-spectrum is given. Moreover, it is shown that the bispectrum (M_fr(X),M_fr(X)(1),M_fr(X)(2), ... ), each term of which is a twisted framed motive of X, has motivic homotopy type of the suspension bispectrum of X. We also construct a compactly generated triangulated category of framed bispectra SH_fr(k) and show that it reconstructs the Morel-Voevodsky category SH(k). As a topological application, it is proved that the framed motive M_fr(pt)(pt) of the point pt = Speck evaluated at pt is a quasi-fibrant model of the classical sphere spectrum whenever the base field k is algebraically closed of characteristic zero.   

The goal of this talk is to present some recent computations of the Picard groups of several spectra of topological modular forms. The first part of the talk will introduce the toolbox, which consists of descent theory and a technical lemma allowing us to compare stable and unstable information in spectral sequences. This is joint work with Akhil Mathew.   

Friday seminar by Annelise Binois 

Yoshiaki Kato,Postdoctoral Fellow , ITA

Tore Selland Kleppe (University of Stavanger) gives a seminar in room 107, 1st floor N.H. Abels House at 14:15 November 11th: Bandwidth Selection In Pre-Smoothed Particle Filters

Yasser Roudi, Group Leader, Kavli Institute for Systems Neuroscience / Centre for Neural Computation, NTU

Marco Matassa (UiO) will give a talk with title: Dirac Operators on Quantum Flag Manifolds

Abstract: I will review the paper "Dirac Operators on Quantum Flag Manifolds" by Ulrich Kr?hmer. The aim is to define Dirac operators on quantized irreducible flag manifolds. These will yield Hilbert space realizations of some distinguished covariant first-order differential calculi.

Friday seminar by Thomas Marcussen

Piyali Chatterjee,Postdoctoral Fellow , ITA

Jeg vil definere Singerkonstruksjonen R_+(M) og gjennomf?re Adams-Gunawardena-Millers bevis av Lins teorem.  

Pia Zacharias,Postdoctoral Fellow , ITA

The Lattice Boltzmann Method and its application in modeling of physiological  flows

Jeg vil snakke om de endelige underalgebraene A(n) i Steenrodalgebraen, analysere A(n)-modulstrukturen til den kontinuerlige kohomologien til Tatekonstruksjonen, og skissere Lin-Davis-Mahowald-Adams' bevis av Lins teorem. 

Friday seminar by Charles Krebs

Kathleen M. Jennings, Fafo Institute for Labour and Social Research