2018 May 14

Combinatorics: Joel Friedman (UBC) "Open Problems Related to the Zeta Functions"

11:00am to 12:30pm


IIAS, Eilat hall, Feldman bldg, Givat Ram
Speaker: Joel Friedman, UBC
Title: Open Problems Related to the Zeta Functions
We express some open problems in graph theory in terms of Ihara graph zeta
functions, or, equivalently, non-backtracking matrices of graphs. We focus
on "expanders" and random regular graphs, but touch on some seemingly
unrelated problems encoded in zeta functions.
We suggest that zeta functions of sheaves on graphs may have relevance to
complexity theory and to questions of Stark and Terras regarding whether
2018 Apr 17

Dynamics seminar: Elon Lindenstrauss (HUJI) - Symmetry of entropy in higher rank diagonalizable actions and measure classification

2:15pm to 3:15pm


Ross 70

The miracle of entropy - that the entropy of a measure preserving transformation calculated forward in time (for T) and backwards in time (for T^{-1}) are equal - is, depending on point of view and the definition used, either a triviality or highly surprising. Entropy theory (of Z-actions) plays a key role in analyzing the rigidity of algebraic (diagonalizable) Z^k actions; I show how a strong version of this symmetry property of entropy is useful in studying the measure classification question for such actions.
Joint work with Manfred Einsiedler.
2018 Apr 10

T&G: Jesse Kass (University of South Carolina), How to count lines on a cubic surface arithmetically

1:00pm to 2:30pm


Room 110, Manchester Building, Jerusalem, Israel

Salmon and Cayley proved the celebrated 19th century result that a smooth cubic surface over the complex numbers contains exactly 27 lines.  By contrast, the count over the real numbers depends on the surface, and these possible counts were classified by Segre.  A number of researchers have recently made the striking observation that Segre’s work shows a certain signed count is always 3.  In my talk, I will explain how to extend this result to an arbitrary field.
2018 Apr 24

T&G: Anton Khoroshkin (HSE), Compactified moduli spaces of rational curves with marked points as homotopy quotients of operads

1:00pm to 2:30pm


Room 63, Ross Building, Jerusalem, Israel
I will explain the notion of a homotopy quotient of an operad providing different examples of operads of compactified moduli spaces of genus zero curves with marked points: including the space of complex curves (math.arXiv:1206.3749), the real loci of the complex one (arXiv:math/0507514) and the noncommutative …