Feb 28

Bounded distance equivalence of aperiodic Delone sets and bounded remainder sets 
Dirk Frettlöh (Bielefeld university)

Delone sets are generalizations of point lattices: unformly discrete
point sets with no large holes. In 1997 Gromov asked whether any
Delone set in the Euclidean plane is bilipschitz equivalent to the
integer lattice . A simpler but stronger condition than bilipschitz
equivalence is bounded distance equivalence. So it is natural to ask
which Delone sets in are bounded distance equivalent to (some scaled
copy of) . This talk gives a gentle introduction to the problem
and presents recent results in this context, mostly for cutandproject
sets on the line. In particular we show a connection between bouded
remainder sets and cutandproject sets that are bounded distance
equivalent to some lattice.

Mar 7

Local limit theorem for inhomogeneous Markov chains (joint with Dolgopyat) 
Omri Sarig (Weizmann Institute)

An inhomogeneous Markov chain is a Markov chain whose state spaces and transition kernels change in time. A “local limit theorem” is an asymptotic formula for probabilities of the form
,
in the limit . Here is a “suitable” sequence of numbers.
I will describe general sufficient conditions for such results.
If time allows, I will explain why such results are needed for the study of certain problems related to irrational rotations.
This is joint work with Dmitry Dolgopyat.

Mar 14

Pathwise derivatives of reflected diffusions 
David Lipshutz (Technion)

Reflected diffusions (RDs) constrained to remain in convex polyhedral domains arise in a variety of contexts, including as heavy traffic limits of queueing networks and in the study of rankbased interacting particle models. Pathwise derivatives of an RD with respect to its defining parameters is of interest from both theoretical and applied perspectives. In this talk I will characterize pathwise derivatives of an RD in terms of solutions to a linear constrained stochastic differential equation that can be viewed as a linearization of the constrained stochastic differential equation the RD satisfies. The proofs of these results involve a careful analysis of sample path properties of RDs, as well as geometric properties of the convex polyhedral domain and the associated directions of reflection along its boundary.
This is joint work with Kavita Ramanan.

Mar 21

Purim 
Holiday


Mar 28

The lower tail for triangles in sparse random graphs 
Wojciech Samotij (TelAviv University)

Let denote the number of triangles in the random graph . The problem of determining the asymptotic of the rate of the lower tail of , that is, the function for a given , has attracted considerable attention of both the combinatorics and the probability communities. We shall present a proof of the fact that whenever , then can be expressed as a solution to a natural combinatorial optimisation problem that generalises Mantel’s / Turan’s theorem. This is joint work with Gady Kozma.

Apr 4

New developments on noncommutative quasicrystals 
Felix Pogorzelski (Universität Leipzig)

The theory of mathematical quasicrystals essentially goes back to work
of Meyer in the 70’s, who investigated aperiodic point sets in
Euclidean space. Shechtman’s discovery of physical quasicrystals (1982,
Nobel prize for Chemistry 2011) via diffraction experiments triggered
a boom of the mathematical analysis of the arising scatter patterns.
Recent years have seen some progress in understanding the geometry,
Fourier theory and dynamics of wellscattered, aperiodic point sets
in noncommutative groups. We explain some of those developments from the viewpoint of approximation of certain key quantities arising from the underlying group actions via a notion of convergence of dynamical systems. One particular focus in this context will be on sufficient criteria to ensure unique ergodicity of the dynamical system associated with a point set.
Based on joint projects with Siegfried Beckus and
Michael Björklund/Tobias Hartnick.

Apr 11

An introduction to warped cones 
Federico Vigolo (Weizmann Istitute)

Warped cones are families of metric spaces that can be associated with actions of discrete groups on compact metric spaces. They were first introduced by John Roe as means of producing interesting examples of metric spaces (in the context of the coarse BaumConnes conjecture), and have since evolved as it turned out that they could be used to construct families of expander graphs and that they were good candidates for a definition of a `coarse geometric’ invariant of actions. In this talk I will introduce the warped cone construction and explain how to use it to obtain expanders. I will then indicate some rigidity results that hold in this settings.

Apr 18

Passover 
Holiday


Apr 25

Passover 
Holiday


May 2

Joint and double coboundaries of transformations an application of maximal spectral type of spectral measures 
Michael Lin (BenGurion University)

Let T be a bounded linear operator on a Banach space X; the elements
of (I − T)X are called coboundaries. For two commuting operators T and
S, elements of (I − T)X ∩ (I − S)X are called joint coboundaries, and those
of (I − T)(I − S)X are double coboundaries. By commutativity, double
coboundaries are joint ones. Are there any other?
Let θ and τ be commuting invertible measure preserving transformations
of (Ω, Σ, m), with corresponding unitary operators induced on L2(m). We
prove the existence of a joint coboundary g ∈ (I − U)L2 ∩ (I − V )L2 which
is not in (I − U)(I − V )L2.
For the proof, let E be the spectral measure on T
2 obtained by Stone’s
spectral theorem. Joint and double coboundaries are characterized using E,
and properties of the maximal spectral type of E, together with a result of
Foia³ on multiplicative spectral measures acting on L2, are used to show the
existence of the required function.

May 9

Independence Day 
Holiday


May 16

students’ probability day  in memory of Oded Schramm 
@ weizmann institute


May 23

On (a,b) Pairs in Random Fibonacci Sequences 
J.C. Saunders (BenGurion University)

We deal with the random Fibonacci tree, which is an inﬁnite binary tree with nonnegative integers at each node. The root consists of the number 1 with a single child, also the number 1. We deﬁne the tree recursively in the following way: if x is the parent of y, then y has two children, namely 
x−y 
and x+y. This tree was studied by Benoit Rittaud who proved that any pair of integers a,b that are coprime occur as a parentchild pair inﬁnitely often. We extend his results by determining the probability that a random inﬁnite walk in this tree contains exactly one pair (1,1), that being at the root of the tree. Also, we give tight upper and lower bounds on the number of occurrences of any speciﬁc coprime pair (a,b) at any given ﬁxed depth in the tree. 

May 30

Open day at the Math department 
(seminar is cancelled)


Jun 6

On the index of refraction of a distribution, lenses and probability. 
Eitan Bachmat (BenGurion University)

We will consider some basic optimization problems and how they relate to optics. We then define an index of refraction to any given distribution. We conjecture an estimate for the index and explain how its related to some natural operations research questions. We also consider lenses and ask questions about the probabilistic behavior of discrete geodesics in a lens setting.

Jun 20

Maximum of exponential random variables and Hurwitz’s zeta function 
Dina Barak (BenGurion University)

A problem, arising naturally in the context of the coupon collector’s problem, is the behavior of the maximum of independent geometrically distributed random variables (with distinct parameters). This question has been addressed by Brennan et al. (British J. of Math. & CS.:8 (2015), 330336). Here we provide explicit asymptotic expressions for the moments of that maximum, as well as of the maximum of exponential random variables with the same parameters. We also deal with the probability of each of the variables being the maximal one.
The calculations lead to expressions involving Hurwitz’s zeta function at certain special points. We find here explicitly the values of the function at these points.
