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Mathematical methods in classical mechanics, classical and quantum field theory, quantum mechanics, statistical mechanics, condensed matter, nuclear and atomic physics.

1 vote

Is the Hessian of Hamilton's function positive-definite?

Shortly after posting my question, I realized that the answer to the original question is that the Hessian is not necessarily positive-definite. In particular, consider picking a different antideriva …
Theo Johnson-Freyd's user avatar
24 votes

Mathematical foundations of Quantum Field Theory

Yes, of course, there is much research on mathematical rigor in quantum field theory. Of course, I don't know what "reasonable", "essentially different", and "realistic" mean to you, but I would say …
Theo Johnson-Freyd's user avatar
8 votes
Accepted

Functor category of quantum field theories?

The question of what "natural transformation of QFTs" should be is a somewhat subtle one. The issue is most apparent if you work with TQFTs, but it doesn't completely go away if you work with dynamica …
Theo Johnson-Freyd's user avatar
3 votes

What do mathematicians currently do in conformal field theory (or more general field theory)

Note that the word "conformal field theory" (indeed, "field theory" in general) has many meanings, depending on the area of mathematics of the user, and in general the relationships between the differ …
Theo Johnson-Freyd's user avatar
2 votes

Stationary phase method on supermanifolds

The stationary phase approximation is strictly easier for fermionic manifolds than for bosonic ones. Indeed, suppose $M = \mathbb{R}^{0|n}$ is a purely odd supermanifold, with (odd) coordinates $x_1,\ …
Theo Johnson-Freyd's user avatar
10 votes
Accepted

Is Segal's notion of conformal field theory a quantum field theory in the sense of Wightman ...

My understanding is that Segal invented his formalism (which was then adapted by Atiyah) by thinking about the same thing Wightman was thinking about: formalising the theory of local operators. In hin …
Theo Johnson-Freyd's user avatar
24 votes
Accepted

What's up with Wick's theorem?

Let's take for granted the Gaussian integration formula, which holds for both bosonic and fermionic integrals, if they are properly interpreted: Theoreom (Gauss, Wick): Let $X$ be a vector space with …
Theo Johnson-Freyd's user avatar
1 vote

Do there exist small neighborhoods in a classical mechanical system without pairs of focal p...

In addition to DBM's (totally correct) answer above, I realized that there's probably a much simpler answer. If I'm wrong, hopefully someone will set me right. Let $\mathcal O$ be an open neighborho …
Theo Johnson-Freyd's user avatar
3 votes

Path integrals outside QFT

Witten, I think, deserves much of the credit for getting mathematicians interested in the path integral, with his paper Quantum field theory and the Jones polynomial. In particular, path integrals ar …
Theo Johnson-Freyd's user avatar
2 votes

Where does a math person go to learn quantum mechanics?

Charles already posted Takhtajan's book, which is my first choice --- it's geared towards early graduate students. A more elementary book, geared towards math undergrads, is by Fadeev (who is, incide …
8 votes

What is Chern-Simons theory?

Some good references are the papers by Dan Freed and the book The geometry and physics of knots by Michael Atiyah. But by far the best answer to your question is in Witten's paper "Quantum field theo …
Theo Johnson-Freyd's user avatar
3 votes

Open symplectic embeddings and deformation quantization

Many definitions I've seen of "star quantization of a Poisson manifold" include the request that each coefficient in $\hbar$ of $a\star b$ be a differential operator in $a,b$. Such a star quantizatio …
Theo Johnson-Freyd's user avatar
16 votes

What is a symplectic form intuitively?

Incidentally, I more or less disagree that symplectic geometry captures what I would consider "classical mechanics". The reason is that in all the examples that I think deserve to be called "classica …
Theo Johnson-Freyd's user avatar
10 votes
Accepted

What are double groups mathematically?

As far as I can tell, a double group is a double cover of a group. Specifically, if $G \subset \operatorname{SO}(n)$ is a group acting by rotations of $n$-dimensional space, its double group is the li …
Theo Johnson-Freyd's user avatar
138 votes
Accepted

What is Quantization ?

As I'm sure you'll see from the many answers you'll get, there are lots of notions of "quantization". Here's another perspective. Recall the primary motivation of, say, algebraic geometry: a geometr …
Theo Johnson-Freyd's user avatar

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