All Questions
13
questions
-2
votes
0
answers
64
views
QED with massless fermions
Consider QED such that physical mass of fermions vanishes. Is it true that their bare mass also vanishes?
- 2,226
3
votes
0
answers
50
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
1
vote
2
answers
188
views
Massless QED modified Lagrangian
Consider a massless theory of QED, with Lagrangian
$$\mathcal{L}_{QED}=
-\frac{1}{4}F_{\mu\nu}F^{\mu\nu}+\bar{\Psi}i\gamma^{\mu}\partial_{\mu}\Psi+
e\bar{\Psi}\gamma^{\mu}A_{\mu}\Psi$$
Is there any ...
- 3,992
1
vote
0
answers
81
views
Minus sign for incoming antifermions
In his Diagrammatica, The Path to Feynman Diagrams (Cambridge University Press, 1994; §4.5 "Quantum Electrodynamics", p. 88), M. Veltman reports the following Feynman rule for incoming ...
- 29
1
vote
0
answers
114
views
Mass shift in QED: perturbative mass terms
This question is similar to Peskin & Schroeder Chap. 7.1 ultraviolet divergence, but my doubt is still unsolved so let me ask the question.
The Peskin & Schroeder explains on p. 221 why the ...
- 353
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 ...
- 97
0
votes
1
answer
257
views
Feynman diagrams with long fermion lines
how do I calculate the interference of these two diagrams, where the fermions are electrons?
The matrix element of the first diagram is calculated as $\frac{1}{(p_3+p_4)^2}\bar{u}(p_2)\gamma_\mu u(...
- 55
0
votes
1
answer
89
views
Virtual fermions vs exclusion principle
How QED eliminates the cases when
in loop corrections two fermions get created with the same momenta and spin state?
Is it done by the ladder operators?
Edit: the two fermions are in two distinct ...
- 324
2
votes
1
answer
753
views
Feynman Propagator for fermionic field $S_F(x-x)=0$
When doing some calculations in my QED course, my tutor used that for
$$S_F(x-y)= - \int \frac{d^4p}{(2\pi)^4}\frac{i( \gamma_{\mu}p^{\mu}+m)}{p^2-m^2+i\epsilon}e^{-ip(x-y)}$$
the Feynman ...
- 63
0
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 ...
- 357
2
votes
1
answer
1k
views
Calculating Feynman amplitude for closed two loop diagrams
Could someone explain or post a link for how one calculates the Feynman amplitudes for closed two loop diagrams?
This is in QED with the same fermion in both loops and a photon connecting them.
6
votes
4
answers
2k
views
How do annihilation and creation operators act on fermions?
I'm taking an introductory course in QFT. During quantization of the Dirac field, my textbook gives a lot of information on how annihilation and creation operators act on vacuum, but nothing about how ...
- 1,356
5
votes
1
answer
432
views
What's the role of field equation in QFT?
For free field theory, it seems the solutions of a field equation are used to give a representation of Poincare group, and the field equation is still satisfied after quantization. However for an ...
- 3,995