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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.

1 vote

Anti-concentration of Gaussian quadratic form

You can directly use Chernoff's inequality, to get $LHS \le e^{-\Lambda^*(\epsilon)}$, where $\Lambda^*(\epsilon) := (\epsilon-1-\log\epsilon)/2$ is the Fenchel-Legendre transform of the log-MGF $\Gam …
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1 vote

Anti-concentration of Gaussian quadratic form

It looks like all the previous answers (including mine) are quite off by a huge margin, if the vector $a=(a_1,\ldots,a_n)$ is somewhat dense in the sense that $\|a\|_1/\|a\|_\infty$ is substantially l …
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1 vote

Practical bounds for the Wasserstein distance in 2 dimensions

There are a few references worth mentioning: https://hal.archives-ouvertes.fr/hal-00915365/document https://www.lpsm.paris/pageperso/bolley/bgv.pdf https://arxiv.org/pdf/1804.10556.pdf Example of …
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1 vote

Marginal density of uniform spherical distribution

Although great answers have already been provided, the one provided below is perhaps be the shortest possible answer to the question. Let $x_1,\ldots,x_k \in \mathbb R$ such that $r_k^2:=\sum_{i=1}^k …
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2 votes
2 answers
443 views

If $0 \le \mu(A) < p < 1$, when is it true that there exists a measurable $B \supseteq A$ su...

Let $(X,\mu)$ be a probability measure space and $A$ be a measurable subset of $X$ such that $0 \le \mu(A) < p < 1$. Question When is it true that there exists a measurable $B \subseteq X$ such that …
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1 vote
1 answer
198 views

Upper bound for $\mathbb P(|f(A+XX^T)-f(A)| > \epsilon)$, where $A$ is a fixed pd matrix and...

Let $A$ be a fixed $n$ by $n$ real symmetric positive definite matrix with eigenvalues $\lambda_1 \ge \lambda_2 \ge \ldots \ge \lambda_n > 0$, and let $f(A):=\sum_{i=1}^n\log\lambda_i$, and let $X$ be …
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1 vote
0 answers
72 views

On the closedness of a certain subset of $\mathbb R$

Let $\mu$ be a probability measure on measurable space $X=\mathbb R^n$ (euclidean), and let $F$ be a family of $\mu$-measurable functions $X \mapsto \mathbb R$ which are uniformly bounded, i.e $b:=\su …
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2 votes

When do 3D random walks return to their origin?

The answer to your question appears to be contained in a 1928 Theorem of Polya, on simple random works on a lattice $\mathbb Z^d$. As a soft-reference, see page 15 of this short paper, using only very …
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1 vote
Accepted

Upper bound for $\mathbb P(|f(A+XX^T)-f(A)| > \epsilon)$, where $A$ is a fixed pd matrix and...

Below, I provide a "high-probability" non-asymptotic bound (see (+) below) based on non-linear Berry-Esseen theory developed by Iosif Pinelis. I'd be grateful if someone would kindly check that I didn …
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0 votes
1 answer
233 views

Anti-concentration: upper bound for $P(\sup_{a \in \mathbb S_{n-1}}\sum_{i=1}^na_i^2Z_i^2 \g...

Let $\mathbb S_{n-1}$ be the unit sphere in $\mathbb R^n$ and $z_1,\ldots,z_n$ be a i.i.d sample from $\mathcal N(0, 1)$. Question Given $\epsilon > 0$ (may be assumed to be very small), what is a r …
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1 vote
Accepted

Anti-concentration: upper bound for $P(\sup_{a \in \mathbb S_{n-1}}\sum_{i=1}^na_i^2Z_i^2 \g...

As pointed out by a user (Nate Eldgredge) in the comments under the question, $$ P\left(\sup_{a \in \mathbb S_{n-1}}\sum_{i=1}^n a_i^2Z_i^2 \ge \epsilon\right) = P\left(\max_{1 \le i \le n}Z_i^2 \ge …
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2 votes
1 answer
186 views

Unconditional lower bound for volume of blowup $\mu(B^\epsilon)$ for $\mu(B) \in (0, 1)$ and...

For a Borel subset $B$ of a metric space $X = (X,d)$ and $\epsilon>0$, recall the defintion of the $\epsilon$-blowup of $B$, namely $B^\epsilon = \{x \in X | d(x,B) \le \epsilon\}$. Let $\mu$ be a pro …
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1 vote
0 answers
89 views

Probability space with countable subset such that every subset of positive measure meets the...

Let $(X, \mathcal F, P)$ be a probability space. Question What kind of condition is this: there exists a sequence $(a_n)_n \subseteq X$ such that $\forall$ measurable $A \subseteq X$, $P(A) > …
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1 vote
0 answers
170 views

Rate of convergence of empirical distribution with respect to Wasserstein distance induced b...

Let $\mathcal X=(\mathcal X, d)$ be a Polish space (i.e complete metric space), and let $\Omega$ be a non-empty subset. Consider the binary cost function $c_\Omega$ on $\mathcal X^2$ defined by $c_\Om …
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0 votes

How to prove that a Brownian bridge $\mathbb{P}(M[0, 1/2]\geq s)\leq 2\mathbb{P}(B(1/2)\geq ...

You can prove it via standard computations. See (2.1), (2.7), and (2.8) of On the maximum of the generalized Brownian bridge.
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