Search Results
| Search type | Search syntax |
|---|---|
| Tags | [tag] |
| Exact | "words here" |
| Author |
user:1234 user:me (yours) |
| Score |
score:3 (3+) score:0 (none) |
| Answers |
answers:3 (3+) answers:0 (none) isaccepted:yes hasaccepted:no inquestion:1234 |
| Views | views:250 |
| Code | code:"if (foo != bar)" |
| Sections |
title:apples body:"apples oranges" |
| URL | url:"*.example.com" |
| Saves | in:saves |
| Status |
closed:yes duplicate:no migrated:no wiki:no |
| Types |
is:question is:answer |
| Exclude |
-[tag] -apples |
| For more details on advanced search visit our help page | |
Results tagged with quantum-field-theory
Search options not deleted
user 86781
Quantum Field Theory (QFT) is the theoretical framework describing the quantisation of classical fields which allows a Lorentz-invariant formulation of quantum mechanics. QFT is used both in high energy physics as well as condensed matter physics and closely related to statistical field theory. Use this tag for many-body quantum-mechanical problems and the theory of particle physics. Don’t combine with the [quantum-mechanics] tag.
0
votes
1
answer
360
views
Is the scalar field operator self-adjoint?
In A. Zee's QFT in a Nutshell, he defines the field for the Klein-Gordon equation as
$$
\tag{1}\varphi(\vec x,t) = \int\frac{d^Dk}{\sqrt{(2\pi)^D2\omega_k}}[a(\vec k)e^{-i(\omega_kt-\vec k\cdot\vec x) …
- 1,507
0
votes
1
answer
228
views
Excitation source in 2D grid coupled harmonic oscillator
In A. Zee's Quantum field theory in a Nutshell, he describes the QFT analogy of a matress, a 2D grid of points $q_a$ connected by springs (first page of first chapter, $q_a$ is the vertical displaceme …
- 1,507
4
votes
1
answer
2k
views
Zee's Nutshell: Feynman diagrams "baby problem": Connected vs. Disconnected
On page 47 of A. Zee's QFT in a Nutshell, he explains how disconnected Feynman diagrams can be built from lower-order connected diagrams:
I don't know how to understand formula $(6)$.
I understand …
- 1,507
2
votes
Accepted
Is a Feynman diagram depicting a vacuum bubble "that gets real" valid?
As explained by @ACuriousMind, even the diagrams with vacuum bubbles that "come to life" are correct Feynman diagrams. However, when one translates the diagrams to actual amplitude terms, these terms …
- 1,507
2
votes
1
answer
880
views
How to separate an exponential with a Hamiltonian with both momentum and position operators?
Statement of exercise
On a page 11 of A.Zee's book QFT in a Nutshell, he derives Dirac's formulation of the path integral formulation of QM for a free particle. This starts with the free particle Ham …
- 1,507
3
votes
1
answer
2k
views
Is a Feynman diagram depicting a vacuum bubble "that gets real" valid?
In exercise I.7.3 of A. Zee's QFT in a Nutshell, we have to draw all the Feynman diagrams of the scalar theory
$$
Z(J) = \int D\varphi e^{i\int d^4x\{\frac 12[(\partial\varphi)^2-m^2\varphi^2]-(\lamb …
- 1,507
7
votes
1
answer
1k
views
What prevents this third-order QED scattering from having a non-zero amplitude?
I have learned that in the Dyson-Wick expansion of the QED scattering operator
$$
S=e^{-i\int_{t_i}^{t_f}H\mathrm{d}t}
$$
with the QED interaction Lagrangian
$$
H=e\bar\psi\gamma^\mu A_\mu\psi
$$
…
- 1,507
3
votes
3
answers
3k
views
Do different creation/annihilation operators always commute?
In a complex (non-hermitian) scalar QFT, is it correct that the creation/annihilation operators $a,a^\dagger$ (particle) and $b,b^\dagger$ (anti-particle) commute, i.e. $[a,b] = [a,b^\dagger] = [a^\da …
- 1,507
11
votes
2
answers
922
views
Why is a minimum field configuration called a vacuum state in SSB?
Most explanations of Spontaneous Symmetry Breaking (SSB) go like this: They take a scalar field Lagrangian with the "Mexican hat" potential $V(\phi)=−10\phi^2+\phi^4$ and argue that since the potentia …
- 1,507
8
votes
1
answer
2k
views
How to show that $\bar\psi\psi$ of a Dirac spinor $\psi$ transforms as a scalar?
I would like to show that for a Dirac spinor $\psi$, the scalar product $\bar\psi\psi$ transforms as a scalar under a Lorentz transformation $\Lambda$, where $\bar\psi = \psi^\dagger\gamma^0$. This is …
- 1,507
11
votes
1
answer
2k
views
How to show that $\bar\psi\gamma^\mu\psi$ of a Dirac spinor $\psi$ transforms as a vector?
This is part 2 of exercise II.1.1 of Zee's QFT in a Nutshell (here's part 1).
This is what I have got:
\begin{align}
\bar\psi\gamma^\lambda\psi \mapsto \bar\psi^{\,\prime}\gamma^\lambda\psi^{\,\prim …
- 1,507
4
votes
0
answers
292
views
What's the connection between the pole contours of propagators and their causality?
Wikipedia distinguishes between three kinds of propagators for a scalar field:
The Retarded propagator's contours have $\mathrm{Im}(k^0)>0$ on both poles, so its limit is completely in the first and …
- 1,507
2
votes
0
answers
556
views
Spin and polarization, QM vs QFT
On page 34 of A. Zee's book QFT in a Nutshell, he states:
I expect you to remember the concept of polarization from your course on electromagnetism. A massive spin 1 particle has three degrees of …
- 1,507
1
vote
0
answers
1k
views
How to Fourier transform creation/annihilation operators?
Zee's QFT in a Nutshell pages 65-66. For a complex scalar QFT
$$
\varphi(\vec{x},t) = \int\frac{d^Dk}{\sqrt{(2\pi)^D2\omega_k}}\left[a(\vec{k})\mathrm{e}^{-i(\omega_kt-\vec{k}\cdot\vec{x})} + b^\dagg …
- 1,507