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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.

2 votes
Accepted

Minimax optimal multiple hypothesis test

Deterministic $\Psi$ is bound to fail. You must randomize. Consider three probability measures supported on $\{1,2\}$. A deterministic $\Psi$ will have only two of the measures in its image. The adver …
Yuval Peres's user avatar
  • 14.2k
7 votes
Accepted

Diameter bound for graphs: spectral and random walk versions

The conjectured inequality is false in General. Proof: Let $\ell=\lfloor n^{1/2}/2 \rfloor$ and let $G_1,G_2,\dots,G_\ell$ be disjoint cliques of size $\ell$. Let $K$ be a clique on $n-\ell^2 >n/2$ …
Yuval Peres's user avatar
  • 14.2k
4 votes

Random spanning trees probability problem

The connection between uniform spanning trees $T$ and stable polynomials used in Fedor Petrov's answer is indeed beautiful, and yields a sharp bound. I want to mention that the slightly weaker bound o …
Yuval Peres's user avatar
  • 14.2k
2 votes
Accepted

Asymptotic properties of weighted random walks / infinite convolutions of random variables

Let $(X_n)_{n\in\mathbb{N}}$ be i.i.d. real random variables and let $0<c<1$. Then the following are equivalent: (a) There exists $r>0$ such that $P(|X_k|>e^{rk} \; \, \text{infinitely often} )=0$. ( …
Yuval Peres's user avatar
  • 14.2k
1 vote

General definition for $k$-dependence of a family of sub-$\sigma$-algebra

One possible definition is to assume a graph structure on the index set, where the maximal degree is $k$. Then you assume that every algebra $\mathcal{F}_i$ is independent of the join of the algebras …
LSpice's user avatar
  • 12.9k
3 votes

Forgery theorem: the Brownian motion stays close to any curve with positive probability

There was part of the hint that you ignored, namely using Levy's construction. To add some detail, the approximation of $S^{n}$ by BM is done recursively in each dyadic interval, rather than globally. …
Yuval Peres's user avatar
  • 14.2k
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|) + …
Michael Hardy's user avatar
2 votes
Accepted

Maximum of a sequence is $o(\sqrt{n})$

First suppose that hypotheses (a) and (b) hold. I will write $w_{i,n}$ instead of $w_i^n$ for clarity. Given $\epsilon>0$, the Monotone convergence theorem implies that there exists $M$ such that $ …
Yuval Peres's user avatar
  • 14.2k
2 votes

Polynomial time mixing Markov chain for multimodal distribution

As noted in the comment by James Martin, some assumption is needed on the Markov chain, e.g., that each step of the chain can be implemented on a Turing machine in polynomial time. The Swendsen-Wang …
Yuval Peres's user avatar
  • 14.2k
5 votes
Accepted

What is the exact definition of a sharp transition?

The parameters $p_n$ are not arbitrary numerical parameters. They represent the expectation of one binary variable in a product space. Changing them additively is very different from changing the powe …
apg's user avatar
  • 640
1 vote

Show that the set of strictly stationary, mean zero and finite variance stochastic processes...

Yes, $\mathcal{P}$ is closed in the spaces \begin{equation} \mathcal{P}_1:=\left\{ X = (X_t)_{t \in \mathbb{Z}} \, : \, \mathbb{E} X_t = 0 \hbox{ and } \mathbb{E}[X_t^2]< \infty, \, \forall\, …
Yuval Peres's user avatar
  • 14.2k
2 votes

Distributions of distance between two random points in Hilbert space

Here is another variation of the fine solution suggested by Mike and made precise by Iosif Pinelis. Let $Z$ be a polish (i.e., separable and complete) metric space with metric $d(\cdot,\cdot).$ Given …
Yuval Peres's user avatar
  • 14.2k
2 votes

Vector version of concentration of Lipschitz functions on sphere (Levy's Lemma)

One can avoid the $n$-dependence. Let $H$ be a Hilbert space, endowed with the norm $\|\cdot\|$. Given $f:\mathbb{S}^{d-1}\to H$ which is $L$-Lipschitz, the goal is to prove a concentration inequalit …
Yuval Peres's user avatar
  • 14.2k
4 votes
Accepted

Local probabilities for lattice random walk

For the one dimensional case, a quite nice bound is in Theorem 4.2 of [1]. See also [2]. The dependence on $\epsilon$ that you seek was first shown by Kesten[3]. The combinatorial approach was revive …
Yuval Peres's user avatar
  • 14.2k
1 vote
Accepted

Bernoulli trials with small dependencies: asymptotics (central limit theorem, law of the ite...

For $0<\beta \le 1/2$, any limiting distribution of the rescaled process $S_n/n^\beta$ will be fully supported in $[-1,1]$, so it will not be normal. The downward drift will imply (using Hoeffding's …
Yuval Peres's user avatar
  • 14.2k

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