All Questions
Tagged with quantum-field-theory symmetry
433
questions
2
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1
answer
107
views
Is the formation of crystal due to internal symmetry or spacetime symmetry?
In the contexts of field theory, we have internal symmetries and spacetime symmetries. Referring to crystal, people would say it is due to space translation symmetry. However, I don't think the ...
- 31
1
vote
0
answers
90
views
Dijkgraaf-Witten for a 2-Group
As a natural extension of my previous question Higher Dijkgraaf-Witten Theory on DW Theory for a 1-form symmetry, we can extend now to 2-groups.
How can we generalize the notion of gauging to a 2-...
- 53
0
votes
1
answer
165
views
What is the connection between the electroweak energy scale and the vacuum expectation value?
I am quite confused about energy scale and vacuum expectation value (VEV). For example, this wiki page says 246Gev is VEV of Higgs field. Does it mean if we go to a higher energy scale (like 24600Gev)...
- 995
3
votes
2
answers
289
views
How to prove a single-point correlation function equal to zero?
A short question, when I am studying QFT-P&S's book, try to use completeness relation (7.2) to expand the two-point correlation function: $$\langle\Omega|\hat T{\phi(x)\phi(y)}|\Omega\rangle\tag{7....
2
votes
1
answer
276
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Higher Dijkgraaf-Witten Theory
I am trying to understand higher-form symmetries in TQFT. In particular the higher-form version of Dijkgraaf-Witten Theory.
It is known that for a 0-form symmetry we can specify the principal G-bundle ...
- 53
2
votes
0
answers
56
views
Gauge-mediated SUSY breaking mechanism explained in simple terms
How can the basics of gauge-mediated SUSY breaking mechanism be explained in simple terms?
(sample explanation of EW SSB, for reference: “electroweak symmetry is broken due to a non-vanishing value of ...
- 127
4
votes
1
answer
234
views
Conformal invariance in 2d and correlation functions
It is well-known that 2d global conformal invariance constrains the 2, 3-point functions to some very simple form, and 4-point function must be
$$
f(\eta, \bar \eta) \prod_{i < j}z_{ij}^{...} \bar ...
- 325
3
votes
1
answer
454
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Translation invariance in QFT
In P&S's QFT book, page 213, the book considered Heisenberg operator's translation under General interacting field:
$$ \begin{aligned}
\left\langle\Omega|\phi(x)| \lambda_{\mathbf{p}}\right\rangle ...
- 1,421
1
vote
0
answers
133
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Symmetry of infinite harmonic oscillators in quantum field theory
We know that the system (Hamiltonian) of $N$ harmonic oscillators possesses $SU(N)$ symmetry, where
\begin{equation}
H=\hbar \omega \sum_{i=1}^{N}\left( a_{i}^{\dagger } a_{i} +\frac{1}{2}\right) .
\...
- 119
2
votes
1
answer
130
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Definition of symmetry factor $p$ in Feynmans diagrams symmetry factor in Coleman's "Introduction to Many-Body Physics"
I'm trying to digest Coleman's 7.2.1 chapter about symmetry factors. Everything is clear up to point 4 where he introduces symmetry factor $p$ as the "dimension of the group of permutations under ...
- 155
0
votes
1
answer
63
views
Wick's Theorem Example from Stoof & Gubbels [duplicate]
I've been learning about Wick's theorem from a variety of sources when I came across this example from "Ultracold Quantum Fields" by Stoof et al. on page 148 (Here I have simplified the ...
0
votes
0
answers
42
views
Commutation relation of $P^{\mu}$ with fermion field $\psi(x)$
On Giunti and Kim's book "Fundamentals of neutrino physics and astrophysics", page 38-39, the book is trying to derive the commutation relation of $P^{\mu}$ and $\psi(x)$.
Begin with:
$$ U\...
- 1,421
2
votes
1
answer
194
views
How common is quantum symmetry?
It is well-known that, if I have a two-dimensional quantum field theory, $\mathcal{Q}$, with a finite, abelian, non-anomalous global symmetry $\Gamma$, and I gauge it, the resulting theory (which I ...
- 4,654
1
vote
1
answer
200
views
Operator Ordering Conventions and Symmetry
Quantization procedures may need operator ordering conventions to avoid ambiguity. In classical theories, classical observables are often described by smooth functions, so the order of observable ...
- 559
3
votes
2
answers
242
views
Why should the generators of a group symmetry annihilate the vacuum state?
I've read in a book that when I have a quantum field theory with a symmetry under a group of transformations generated by a basis of generators, these generators should annihilate the vacuum state $\...
- 159