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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.

4 votes
1 answer
2k views

When does the ratio X/Y of two random variables have a finite moment-generating function?

Let $X$ and $Y$ be two positive random variables with $Y < X$; these may be highly correlated. I would like a reasonable condition on $X$ and $Y$ so that the ratio $X/Y$ has a finite moment-generatin …
Tom LaGatta's user avatar
  • 8,532
11 votes
3 answers
5k views

Strong law of large numbers for weakly dependent random variables

Let $X_i$ be a sequence of identically-distributed random variables with finite-range dependence (i.e. there exists $I$ such that if $|i-i'| \ge I$, then $X_i$ and $X_{i'}$ are independent), and a fin …
Tom LaGatta's user avatar
  • 8,532
0 votes
1 answer
161 views

Ratios of random variables with weak moment condition

Let $X_n$ be a sequence of iid positive random variables. Assume that $X_n$ has finite $\alpha$th moment for some value $\alpha \in (0,1)$, but infinite first moment. Assume also that the reciprocal $ …
Tom LaGatta's user avatar
  • 8,532
6 votes
1 answer
4k views

Conditioning on one term of a sum of random variables

Let $\theta$ be normally distributed with mean $\bar \theta$ and variance $s^2$. Let $Z$ be normally distributed with mean $0$ and variance $\sigma^2$, and chosen independently of $\theta$. Define $ …
Tom LaGatta's user avatar
  • 8,532
5 votes
0 answers
536 views

Conditional probabilities in Banach spaces

This is the infinite-dimensional sequel to my question, Conditional probabilities are measurable functions - when are they continuous?. Let $\Omega = \Omega_1 \times \Omega_2$ be a probability space …
Tom LaGatta's user avatar
  • 8,532
6 votes
2 answers
3k views

Dense inclusions of Banach spaces and their duals

(This is the abstract Wiener space construction due to Gross, hence the [pr.probability] tag) If we associate $H$ with its dual $H^{\star}$, we have the inclusions $$X^{\star} \hookrightarrow H^{\star …
Tom LaGatta's user avatar
  • 8,532
4 votes
2 answers
2k views

Convergence of Gaussian measures

Let $X$ be a separable Banach space with its Borel $\sigma$-algebra $\mathcal F$. Let $x_n \to x$ in $X$. Fix a Gaussian covariance operator $K$, and let $\mathbb P_n$ and $\mathbb P$ be Gaussian me …
Tom LaGatta's user avatar
  • 8,532
3 votes
1 answer
4k views

Derivatives of conditional expectations

Let $X$, $Y$ and $Z$ be independent, real-valued random variables, probably with continuous density functions. Define $A = X + Y$ and $B = X + Z$. Consider the regular conditional expectation $E_Y(a …
Tom LaGatta's user avatar
  • 8,532
5 votes
1 answer
399 views

Is every bornological space measurable?

Every topological space is measurable, since we may canonically equip a topological space with its Borel $\sigma$-algebra. A bornological space is like a topological space, except the structure descri …
Tom LaGatta's user avatar
  • 8,532
3 votes
1 answer
958 views

When is the support of a Radon measure separable?

Let $X$ be a topological space, equipped with its Borel $\sigma$-algebra $\mathcal B(X)$, and let $\mathbb P$ be a Radon probability measure on $(X, \mathcal B(X))$. Recall that the support of the mea …
Tom LaGatta's user avatar
  • 8,532
17 votes
5 answers
3k views

Conditional probabilities are measurable functions - when are they continuous?

Let $\Omega$ be a Banach space; for the sake of this post, we will take $\Omega = {\mathbb R}^2$, but I am more interested in the infinite dimensional setting. Take $\mathcal F$ to be the Borel $\sig …
Tom LaGatta's user avatar
  • 8,532
1 vote
2 answers
482 views

The limiting behavior of geometric random walk

I would like to know what the asymptotic limiting behavior is for the following random walk on $\mathbb Z^d$. By Donsker's invariance principle, I suspect that its behavior is diffusive, i.e., the dis …
Tom LaGatta's user avatar
  • 8,532
5 votes
1 answer
743 views

Cameron-Martin theorem for non-Gaussian measures

Let $X$ be a locally convex topological linear space, and $\mathbb P$ be a probability measure on $X$. Denote the mean vector $m \in X$ and covariance operator $k : X^* \to X$. Let $\tau_u : X \to X$ …
Tom LaGatta's user avatar
  • 8,532
3 votes
0 answers
235 views

Is every covariance operator the covariance of a measure?

Let $X$ be a topological linear space over $\mathbb R$ which is complete and Hausdorff with a dual space that separates points. Let $k : X^* \to X$ be an arbitrary covariance operator. i.e., any conti …
Tom LaGatta's user avatar
  • 8,532
1 vote
1 answer
350 views

Agreement of two topologies on a linear space

I'm dealing with the formalism of an abstract Wiener space, and I'm not sure if two relevant topologies coincide. Let $X$ be a topological vector space, and let $X^*$ be its dual space of continuous …
Tom LaGatta's user avatar
  • 8,532

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