BGU Probability and Ergodic Theory (PET) seminar Ical Atom

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 Z^2. A simpler but stronger condition than bilipschitz equivalence is bounded distance equivalence. So it is natural to ask which Delone sets in R^d are bounded distance equivalent to (some scaled copy of) Z^d. This talk gives a gentle introduction to the problem and presents recent results in this context, mostly for cut-and-project sets on the line. In particular we show a connection between bouded remainder sets and cut-and-project sets that are bounded distance equivalent to some lattice.

An inhomogeneous Markov chain $X_n$ 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

$Prob[S_N-z_N\in (a,b)]$, $S_N=f_1(X_1,X_2)+....+f_N(X_N,X_{N+1})$

in the limit $N\to\infty$. Here $z_N$ 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.

Let $X$ denote the number of triangles in the random graph $G(n,p)$. The problem of determining the asymptotic of the rate of the lower tail of $X$, that is, the function $f_c(n,p) = log Pr(X ≤ c E[X])$ for a given $c ∈ [0,1)$, has attracted considerable attention of both the combinatorics and the probability communities. We shall present a proof of the fact that whenever $p >> n^{-1/2}$, then $f_c(n,p)$ 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.