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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 …
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
$$E\max(X,Y)=E|X-Y|/2\leq \frac{1}{2} (E|X|+E|Y|)=E|X|=\sqrt{2/\pi}\sim 0.798$$ …
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, $1\leq r \leq 2$. …
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 …
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 …
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 …
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 …
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 …
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| …
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 …
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 …
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 $n$.
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 …
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 …
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 …