2019 Dec 05

Colloquium: Yoel Groman (HUJI) - Floer homology of the magnetic cotangent bundle

2:30pm to 3:30pm


Manchester Building (Hall 2), Hebrew University Jerusalem

Hamiltonian Floer cohomology was invented by A. Floer to prove the Arnold conjecture: a Hamiltonian diffemorphism of a closed symplectic manifold has at least as many periodic orbits as the sum of the Betti numbers. A variant called Symplectic cohomology was later defined for certain non compact manifolds, including the  cotangent bundle of an arbitrary closed smooth manifold. The latter is the setting for classical mechanics of constrained systems.

2019 Nov 06

Logic Seminar - Itay Kaplan

11:00am to 1:00pm


Ross building - Room 63
On distal and co-distal types


I will define the notions described in the title, and ask if they are equivalent. I will present a proof showing that they are in case the theory is NIP. The proof is essentially the proof of the fact that the lack of distality is witnessed by a sequence of singletons by Pierre Simon’s.
2019 Nov 04

NT & AG Lunch: Michael Temkin, "Resolution of singularities"

Repeats every week every Monday until Sun Dec 15 2019 .
1:00pm to 2:00pm

1:00pm to 2:00pm
1:00pm to 2:00pm
1:00pm to 2:00pm
1:00pm to 2:00pm
1:00pm to 2:00pm


Mathematics, Faculty Lounge
This semester will be devoted to resolution of singularities -- a process that modifies varieties at the singular locus so that the resulting variety becomes smooth. For many years this topic had the reputation of very technical and complicated, though rather elementary.
In fact, the same resolution algorithm can be described in various settings, including schemes, algebraic varieties or complex analytic spaces.
2019 Dec 10

Boris Solomyak (BIU) Hoelder regularity for the spectrum of translation flows

2:00pm to 3:00pm

Abstract: We consider generic translation flows corresponding to Abelian differentials on flat surfaces of genus $g\ge 2$. These flows are weakly mixing by the Avila-Forni theorem. Recently Forni obtained Hoelder estimates on spectral measures for almost all translation flows, following earlier work by Bufetov and myself in genus two. Combining Forni's idea with our methods, we extended our proof to the case of arbitrary genus $g\ge 2$. It is based on a vector form of the Erd\H{o}s-Kahane argument, which I will try to explain.
This is a joint work with A. Bufetov.
2019 Oct 30

Logic Seminar - Eugenio Colla

11:00am to 1:00pm


Ross 63
Model-theoretic proofs of partition theorems for semigroups.

Partition theorems have the following form. Let "regular" be some notion for a structure S; theorem: for every finite partition of S there is a "regular" set inside a cell of the partition. 
2019 Nov 05

T&G: Andrei Caldararu (UW Madison), A survey of categorical enumerative invariants

1:00pm to 2:30pm


Room 209, Manchester Building, Jerusalem
I will survey recent progress in defining and computing categorical enumerative invariants, analogues of Gromov-Witten invariants defined directly from a cyclic A_infinity category and a choice of splitting of the Hodge filtration on its periodic cyclic homology. A proposed definition of such invariants appeared in 2005 in work of Costello, but the original approach had technical problems that made computations impossible.
2019 Nov 07

Basic Notions: Wayne Horowitz (HUJI, Archaeology department) "Some themes in Babylonian Mathematics of Astronomy".

4:00pm to 5:15pm


Ross 70
Today, in our modern world, we perceive the physical universe in mathematical terms; whether degrees on longitude and latitude on earth, or in units of space-time beyond our earthly horizons. This talk will present two ancient cuneiform tablets from Babylonia which offer a geometric impression of the physical world as experienced by ancient Babylonians. Comparisons will be made with a range of other ancient mathematical, geographic, and astronomical materials from the cuneiform Ancient Near East.
2019 Nov 07

Groups & Dynamics seminar: Alex Margolis (Technion) “Almost normal subgroups and quotient spaces״

10:00am to 11:00am


Ross 70
Abstract: A subgroup is said to be almost normal if it is commensurable
to all of its conjugates. Even though there may not be a well-defined
quotient group, there is still a well-defined quotient space that admits
an isometric action by the ambient group. We can deduce many geometric
and algebraic properties of the ambient group by examining this action.
In particular, we will use quotient spaces to prove a relative version
of Stallings-Swan theorem on groups of cohomological dimension one. We