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

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
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
17 votes

Meaning of a quantum field given by an operator-valued distribution

tl;dr: The reason for operator-valued distributions is because the physically meaningful "measurements" in QFT are things that preserve locality and that can be measured at any location. In quantum m …
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
13 votes

Grothendieck group of the category of boundary conditions of topological field theory

To understand the possible spaces of boundary conditions for a TQFT, it is helpful to start in highest dimension. Suppose you have a $(d+1)$-dimensional nonanomalous TQFT $\mathcal Q$. (The anomalous …
Theo Johnson-Freyd's user avatar
5 votes
Accepted

Supersymmetry charge $Q$ as anti-linear and anti-unitary operator

Suppose you are given a super Hilbert space $\mathcal{H} = \mathcal{H}_0 \oplus \mathcal{H}_1$, with bosonic and fermionic subspaces $\mathcal{H}_0$ and $\mathcal{H}_1$ respectively. Define a new supe …
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 …
Ilmari Karonen's user avatar
21 votes

Fully extended TQFT and lattice models

It may take a bit of extraction, but positive answers to both of your questions follow from my results joint with Gaiotto in Condensations in higher categories (arXiv:1905.09566). In that paper we bui …
David Roberts's user avatar
  • 35.5k
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
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 …
Eric Peterson'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 …
Michael Albanese'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 …
Willie Wong's user avatar
  • 39.1k
3 votes

Quantization of a classical system (e.g. the case of a billiard)

As to the bulk of your question, which I take to be a reference request for mathematical accounts of quantum mechanics, I am partial to the book Quantum Mechanics for Mathematicians by L. Takhtajan. …
Community's user avatar
  • 1
4 votes

Quantization of a classical system (e.g. the case of a billiard)

Quantization is not a functor.
Community's user avatar
  • 1
35 votes

Quantum dynamics on varieties and Salmon Prizes

I can't comment on the Lion hypotheses. I'm pretty sure the SHLT is nothing more than the fact that: A linear endormophism of a $k$-dimensional vector space factors through a $(k-1)$-dimensional …
Theo Johnson-Freyd's user avatar

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