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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.
56
votes
Accepted
What is a cumulant really?
Cumulants have many other names depending on the context (statistics, quantum field theory, statistical mechanics,...): seminvariants, truncated correlation functions, connected correlation functions, …
45
votes
What are the big problems in probability theory?
Maybe the no1 problem of probability is to make rigorous what one finds in just about any textbook in statistical mechanics. In other words it is to put the predictions of Wilson's renormalization gro …
33
votes
Integration of a function over 7-sphere
The result is
$$
I(k)=\frac{2\pi^4\ \Gamma\left(\frac{k}{2}+1\right)\Gamma\left(\frac{k}{2}+2\right)}{\Gamma(k+4)}\ ,
$$
which can be simplified a bit more using the Legendre Duplication Formula.
More …
31
votes
Why is Quantum Field Theory so topological?
The framing of your question is a bit ambiguous and perhaps there are two different questions
here depending on the context and interpretation. One could approach your question from the point of view …
30
votes
What mathematical treatment is there on the renormalization group flow in a space of Lagrang...
Dec 2017 edit: I just put a hopefully useful detailed complement to this post on https://physics.stackexchange.com/questions/372306/wilsonian-definition-of-renormalizability
The answer to your ques …
30
votes
A roadmap to Hairer's theory for taming infinities
Let me comment on points 4) and 5). The problem with infinities in QFT or traditional equilibrium statistical field theory
is related to the one addressed by Martin's theory but there are some differe …
26
votes
Central limit theorem via maximal entropy
There is a book on the subject: "Information Theory and The Central Limit Theorem" by Oliver Johnson.
The article by Anshelevich mentioned by Yemon considers the operator $T$ acting on probability den …
21
votes
Determinant of the random matrix $X^2+Y^2$
This is easy to do using a graphical calculus for contractions of old-fashioned tensors. See this recent article for an example of application of such techniques and hopefully useful references.
Here …
18
votes
Why is conformal invariance only possible for massless theories?
It's not clear from the post if you are talking about classical or quantum field theories. In QFT, conformal invariance implies scale invariance. If the theory has a mass $m$ then, as John explained, …
16
votes
Positivity of certain Fourier transform
I think the result goes back to Polya, see "Some theorems on stable processes" by Blumenthal and Getoor. Another reference is Paul Lévy "Sur une application de la dérivée d’ordre non entier au calcul …
13
votes
Gaussian distributions as fixed points in Some distribution space
Indeed, as J.C. said this has to do with the renormalization group (RG) which in the present context is a transformation $\mu\rightarrow \mu\ast\mu$ followed by rescaling by $\sqrt{2}$ to keep the var …
10
votes
Free Boson Correlator $ \langle X(z)X(w) \rangle =- \ln |z - w| $
My answer Wiener measure and Bochner Minlos can help defining a free massless real scalar field as a random element of $S_0'(\mathbb{R}^2)$. Namely, take the Schwartz space of rapidly decaying test fu …
9
votes
Wiener measure and Bochner Minlos
Yes. Wiener measure can be arrived at using the Bochner-Minlos Theorem in at least two ways.
One can consider the bilinear form on $S(\mathbb{R})$
$$
C(f,g)=\int_{\mathbb{R}}\ \overline{\widehat{f} …
9
votes
Accepted
No kernel of the form $\lvert x - y\rvert^{-1}$ on tempered distributions?
Yes it is possible. Let $K\in S'(\mathbb{R}^2)$ be the distribution acting on test functions $f(x,y)$ by
$$
K(f)=\int_{|x-y|\ge 1} \frac{f(x,y)}{|x-y|}\ dx\ dy
\ + \int_{|x-y|< 1} \frac{f(x,y)-f(x,x)} …
8
votes
Accepted
How do you know that you have succeeded-Constructive Quantum Field Theory and Lagrangian
The axioms don't tell you what theory you constructed. For that you need to go beyond the construction of correlation functions of the elementary field $\phi$ (the basic chapter on renormalization in …