All Questions
Tagged with quantum-field-theory fermions
399
questions
-2
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64
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QED with massless fermions
Consider QED such that physical mass of fermions vanishes. Is it true that their bare mass also vanishes?
- 207k
5
votes
2
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413
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Explicit quantization of free fermionic field
The canonical quantization of a scalar field $\phi(x)$ can explicitly be realized in the space of functionals in fields $\phi(\vec x)$ (here $\vec x$ is spacial variable) by operators
\begin{eqnarray}
...
CommunityBot
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1
vote
1
answer
57
views
What happens to the fermion spin when I move around it in a full circle
I would like to understand the actual meaning of the description of a fermion as a spinor. I have a background in QFT and understand the calculations, but there is a leap to the actual experiment ...
- 1,734
0
votes
1
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73
views
$2\pi$-rotation of fermionic states vs. fermionic operators
Given a fermionic state $|\Psi\rangle$, a $2\pi$ rotation should transform it as
\begin{equation}
|\Psi\rangle \quad\to\quad -|\Psi\rangle \,,
\end{equation}
On the other hand, given a fermionic ...
- 207k
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Questions about fundamental solutions and propagators for the Dirac operator
I thought that propagator is a synonym for fundamental solution. But that seems not to be the case since in this answer it is said that an expression with delta function on a surface has to be ...
- 207k
1
vote
1
answer
519
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Generating Functional and 4-point Correlation Function for $\phi \psi \rightarrow \phi \psi$ scattering in Yukawa Theory
I want to compute, using the generating functional method, the 4-point correlation function $G^{(4)}(x_1,x_2,x_3,x_4)$ for the Lagrangian
$$
\mathcal{L} [\phi, \psi, \chi] = \overline{\chi} ( i \...
CommunityBot
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3
votes
0
answers
49
views
Field strength renormalization for fermions
Following section 7.1 and 7.2 in Peskin and Schroeder (P&S), I've tried to consider what the derivation of the LSZ formula looks like for (spin $1/2$) fermions (in the text, they explicitly ...
- 863
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answers
77
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Application of Callias operator in physics
In his article "Axial Anomalies and Index Theorems on Open Spaces" C.Callias shows how the index of the Callias-type operator on $R^{n}$ can be used to study properties of fermions in the ...
- 6,744
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31
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How to derive Fermion Propagator for Special Kinetic Term?
I am currently working through chapter 75 of the book on QFT by Srednicki. There, he considers the example of a single left-handed Weyl field $\psi$ in a $U(1)$ gauge theory. The Lagrangian, written ...
- 207k
1
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0
answers
40
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Regarding vanishing of a triangle diagram
Furry's theorem ($C$ symmetry) is very important in calculations in QCD, Electroweak theory. Primarily it says everything about QED (three photon triangle diagram), but can be extended to QCD, and ($Z$...
- 207k
8
votes
1
answer
529
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Does the massless fermion in $2+1$ dimensions suffer from gauge anomaly?
In Fermion Path Integrals And Topological Phases Witten showed that for a massless Dirac fermion in $2+1$ dimensions
$$S[\bar{\psi},\psi]=\int d^{3}x\bar{\psi}iD\!\!\!\!/_{A}\psi,$$
where $A$ is a $...
CommunityBot
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votes
1
answer
59
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Exact definition of topological non-identical diagrams
It is often said that Feynman diagrams for fermions do not have symmetry factors.
Consider I have a spinless fermionic quantum many-body system with Hamiltonian:
$$H=\int_{r}\psi^{\dagger}(r)\frac{\...
- 534
2
votes
2
answers
229
views
Order of spinors in an equation for a Feynman diagram or contraction
I'm going over scattering theory in Peskin and Schroeder book, in his chapter on fermion scattering he wrote a specific contraction and the equation describing it
One thing he didn't mention is the ...
CommunityBot
- 1
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votes
1
answer
198
views
Single chirality electron and photon interaction
I asked a similar question about QED Lagrangian but I guess the question wasn't clear enough since I didn't get any correct answers. So, I'll try to ask the question in a different way: how does one ...
CommunityBot
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-2
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2
answers
874
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Fermion Determinant [closed]
When we calculate fermion determinant for either Majorana or Weyl spinors, why do we get an extra factor of half in the coefficient of the determinant as compared to the Ghost determinant?
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