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Theory and applications of probability and stochastic processes: e.g. central limit theorems, large deviations, stochastic differential equations, models from statistical mechanics, queuing theory.

21 votes

A roadmap to Hairer's theory for taming infinities

There are several treatments of Hairer's theory, including lecture notes of his that try to give the "big picture". Brief answers to some of your questions: 1) Those are the solutions to the underl …
ofer zeitouni's user avatar
17 votes

Maximum of two normal random variables

First, an upper bound that beats your second bound is the following: use the equality $$\max(a,b)=(a+b+|a-b|)/2.$$ Then $$E\max(X,Y)=E|X-Y|/2\leq \frac{1}{2} (E|X|+E|Y|)=E|X|=\sqrt{2/\pi}\sim 0.798$$ …
ofer zeitouni's user avatar
17 votes
Accepted

Rate of convergence in the Law of Large Numbers

An early occurence of such bounds is in the theorem of Theorem of vonBahr and Eseen vonBahr, B., Esseen C.-G.: Inequalities for the rth absolute moment of a sum of random variables, $1\leq r \leq 2$. …
ofer zeitouni's user avatar
16 votes
Accepted

Laws of Iterated Logarithm for Random Matrices and Random Permutation

My initial answer was wrong. Instead of completely deleting it, I left it at the bottom of the post. I use notation now that slightly differ from my original post. As before, I give only a partial a …
ofer zeitouni's user avatar
14 votes
Accepted

What is "tilting" in the context of large deviations?

Tilting refers to a change of measure of the form $e^{\lambda \cdot x}/C(\lambda)$ where $C(\lambda)=E(e^{\lambda\cdot X})$. (The setup is that the measure for which you are proving large deviations i …
ofer zeitouni's user avatar
11 votes
Accepted

Shortest path through $\sqrt{n}$ points out of $n$

The following is a partial answer. It is useful to rescale. So think of a Poisson process in the plane and consider the box of side $n$. There will be roughly $n^2$ points there. Let $A_{[a,b]}$ be …
ofer zeitouni's user avatar
11 votes
Accepted

Repeated random two-steps in $\mathbb{R}^3$: unbounded?

I assume your random $M_i$s are from $O(3)$, not $SO(3)$. In fact, I suspect that the answer depends on whether $M_1M_2$ has eigenvalue $1$ or eigenvalue $-1$. If I did not make a mistake, when you e …
ofer zeitouni's user avatar
10 votes
Accepted

Harmonic Crystal using Random Walk

The object you look at is called the Gaussian Free Field (on your graph, with zero boundary conditions) in dimension $2$. There is a lot known about it. For some pointers see the Wiki page http://en.w …
ofer zeitouni's user avatar
9 votes

Probability that planar Brownian motion doesn't "encircle" 0

Divide the interval $[|x|,1]$ into $-\log_2 |x|$ intervals $[r_i,r_{i+1}]$. Radially, the BM performs a (simple) random walk between the circles of these radii, and there will be at least $-\log_2 |x| …
ofer zeitouni's user avatar
9 votes
Accepted

Maxima of Brownian motion

A good way to measure the set of maxima is the Hausdorff dimension of the set of records, which for BM is a.s. 1/2. Because of time/scale invariance, the dimension is the same for $\alpha B_\cdot$, an …
ofer zeitouni's user avatar
8 votes
Accepted

Is there a McDiarmid-type inequality for sequences with a finite range of dependence?

There are several versions of this type: 1) K. Marton has results for dependent variables. Maybe closest to what you ask (for convex functions $f$) is the paper of Samson: Samson paper 2) For a mart …
ofer zeitouni's user avatar
7 votes
Accepted

Probability all Bernoulli random variables take value $1$ with limited independence

This has been treated in the literature: http://arxiv.org/pdf/0801.0059v3.pdf also see http://arxiv.org/pdf/1201.3261.pdf In particular, the upper bound goes to 0, but only polynomialy in $n$.
ofer zeitouni's user avatar
7 votes
Accepted

Positive correlation of conditional expectations

Of course not. Let $X,Y$ be negatively correlated centered standard Gaussian (say with correlation -1/2). Let $Z=X+Y$ and let ${\cal A}=\sigma(X)$, ${\cal B}=\sigma(Y)$. Then $E(Z|{\cal A})=X+E(Y|{\ca …
ofer zeitouni's user avatar
7 votes
Accepted

Concentration of sum of powers of normals

For $p>1$, the random variables you discuss do not possess exponential moments; You are in the regime of large deviations with stretched exponential tails. See for example the following recent paper b …
ofer zeitouni's user avatar
7 votes

Connections between martingales and Fourier analysis

There are links, for example in the theory of singular integrals, see section 6.2 in Stroock's book on probability theory. Also, googling "BMO and martingales" will give you information in the directi …
ofer zeitouni's user avatar

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