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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.

67 votes

Why do probabilists take random variables to be Borel (and not Lebesgue) measurable?

One reason is that probabilists often consider more than one measure on the same space, and then a negligible set for one measure (added in a completion) might be not negligible for the other. The sit …
Yuval Peres's user avatar
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26 votes
Accepted

A variation of the law of large numbers for random points in a square

Given $n^2$ i.i.d. uniform points in $[0,1]^2$, the goal is to draw a configuration of $cn$ vertical lines and $cn$ horizontal lines such that in each small rectangle there is at most one marked point …
Yuval Peres's user avatar
  • 14.2k
23 votes

Size of largest square divisor of a random integer

The asymptotic frequency of square-free integers is known to be $6/\pi^2$, see [1]. Denote by $P_n$ the uniform distribution on $[1,n]$ and by $E_n$ the corresponding expectation. Then $$E_n(r)=\sum_{ …
Yuval Peres's user avatar
  • 14.2k
19 votes

What makes Gaussian distributions special?

If the random vector $(X,Y)$ in the plane has independent coordinates and a rotation-invariant distribution, then it is Gaussian.
16 votes
Accepted

Expected value of biggest distance of adjacent points uniformly picked in $[0,1]$

The expected value is asymptotic to $(\log n)/n$ as $n$ tends to infinity (By "asymptotic" I mean that the ratio tends to 1). One way to see this is to use the representation of order statistics of un …
Yuval Peres's user avatar
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15 votes
Accepted

How many people have the same exact number of hairs?

This question has been studied extensively in the computer science literature under the name "balls in bins"; see [1] which gives quite tight bounds in Theorem 1, page 161 and also describes prior wo …
Yuval Peres's user avatar
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11 votes
Accepted

Recursive random number generator based on irrational numbers

Of course the $X_k$ are not independent as random variables. So I assume you are referring to some notion of asymptotic independence, and it would help if you state your conjecture more precisely. One …
Yuval Peres's user avatar
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11 votes
Accepted

Concentration bounds for martingales with adaptive Gaussian steps

Observe that $X_n=X_{n-1}(1+Z_n)$ where $\{Z_k\}_{k \ge 1}$ are i.i.d. standard normal. Hence to analyze the asymptotic distribution of $|X_n|$, pass to logarithms, to get $$\log(|X_n|)= \log(|X_1|) + …
Yuval Peres's user avatar
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11 votes

The Wiener measure of an open set

This is known as the support theorem for Brownian motion. Besides the proof in the answer of Iosif Pinelis and the proof in Exercise 1.8 of [1], there is also a proof on page 59 of [2]. Generalization …
Yuval Peres's user avatar
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10 votes

Measure of intersections in probability spaces

The answer is negative: It is possible that there is no good choice of $i,j$. Let $T$ be a uniform spanning tree in the infinite ladder ${\bf Z} \times \{0,1\}$. To be precise, this is a weak limit o …
Yuval Peres's user avatar
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10 votes

Series involving power of the index

The Borel distribution with parameter $x \in [0,1]$ is given by $$p_n= \frac{e^{-x n}(x n)^{n-1}}{n!}\,.$$ for $n \ge 1$. This distribution represents the probability that in a Galton Watson branchin …
Yuval Peres's user avatar
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10 votes
Accepted

Can Birkhoff's ergodic theorem for integrable functions easily be deduced from Birkhoff's er...

There is a simple reduction of the Birkhoff ergodic Theorem for $L^1$ functions to the bounded case using Kakutani-Rokhlin towers, that I learned from H. Furstenberg and B. Weiss decades ago. We use …
Yuval Peres's user avatar
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10 votes

Expected value of non-negative iid random variables

The canonical argument proving the upper bound is in the comment by Mathworker21, which has now been posted as an answer. I just want to add that the constant $e$ obtained there is sharp. Indeed, if …
Yuval Peres's user avatar
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9 votes
Accepted

Largeness of the set of zeroes of a Brownian motion

Yes, the local time (at zero) maps the zero set of Brownian motion to an interval. See e.g. Lemma 6.9 page 159 in [1] for continuity. [1] Brownian motion, by Peter Mörters and Yuval Peres. Cambridge U …
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9 votes
Accepted

Average and max. hitting time to a specific vertex

Notation: Let $G=(V,E)$ be an undirected simple graph of $n$ nodes. If $\tau_x$ is the (random) time it takes the walk to reach the node $x$, then write $H(v,x)=E_v(\tau_x)$. Denote $H_{\max}(x):=\m …
Yuval Peres's user avatar
  • 14.2k

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