All Questions
Tagged with quantum-electrodynamics field-theory
41
questions
0
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0
answers
51
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QED without fermions? [duplicate]
Is it possible to write down a sensible analog to QED but without fermions? Or better yet, with only scalar particles? Would two scalar fields with an interaction term $\lambda \phi_1 \phi_2^2$ lead ...
- 2,504
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0
answers
54
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Is completeness relation of polarization vector equivalent to propagator?
For the Proca Lagrangian:
$$\mathcal{L}=-\frac{1}{4}F_{\mu \nu}F^{\mu \nu}+\frac{1}{2}m^{2}A_{\mu}A^{\mu}$$
the equation of motion is:
$$\Box A^{\mu}-\partial^{\mu}\partial_{\nu}A^{\nu}+m^{2}A^{\mu}=0$...
- 567
1
vote
1
answer
147
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How particles interact with the electromagnetic potential $A^\mu$?
It is well known that one reason quantum mechanics started to being developed, was because scientist wanted a model to explain electron orbits in atoms.
Borh interpreted that the for orbits to exist ...
- 1,525
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48
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Ward identity in scalar QED; gauge transformations & plane wave solutions for polarization
I am prepping for my QFT2 exam tomorrow, and in one of the mock exams I found the following question (and I'm not quite sure how to go about this). Given the following Lagrangian:
$$
L = -\frac{1}{4}...
0
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0
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98
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Why is the source of the EM Field in QED the probability current and not the electric current?
I have some problems understanding the interaction term in the QED Lagrangian. If we take
$$
\mathcal{L} = -\frac{1}{4}F_{\mu\nu}F^{\mu\nu} + \bar \psi (\gamma^\mu\partial_\mu-m)\psi+\bar \psi \gamma^\...
- 29
1
vote
0
answers
66
views
In Peskin & Schroeder's QFT book page 704, the definition of electric charge is opposite?
In Peskin's book Chapter 4, the QED Lagrangian in Eq.(4.3) which contains the interaction term $$\mathcal{L}_{\mathrm{int}}=-q\bar{\psi}\gamma^\mu\psi A_{\mu}\tag{4.3}.$$ From this Lagrangian we can ...
- 19
2
votes
1
answer
162
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Physical states in Gupta-Bleuler quantization
I'm reading Timo Weigand notes for Gupta-Bleuler quantization of free EM field.
On page 109, Author has made the following statements.
The Gupta-Bleuler condition for physical state is
$$|\vec{p},\...
- 69
1
vote
2
answers
289
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Mathematically, what's the difference between the EM field in classical E&M and the EM field in QED?
Perhaps another way to put it is, what exactly does it mean to quantize the EM field and why is it necessary? What mathematical properties does the quantized version of the field have that the ...
- 2,327
1
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0
answers
194
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Path integral quantization of QED [closed]
I am trying to derive the correlation functions in QED within the path integral formalism. As we know, the QED Lagrangian is given by
\begin{align}
\mathcal{L}_{\mathsf{QED}} = \bar{\psi}(...
1
vote
1
answer
87
views
Does single electron interact with its own electromagnetic field?
The QED equations are given by
$\square A^\mu=e\bar{\psi}\gamma^\mu\psi$
$i\gamma^\mu\partial_\mu\psi=(m+e\gamma^\mu A_\mu)\psi$
These equations suggest, that electrons interact with field created by ...
- 925
1
vote
0
answers
54
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Question on positronium lifetime
From Wikipedia I could get that lifetime of orthopositronium (spin of electron and positron point in same direction) is
$t=\frac{9h}{4m_ec^2\alpha^6(\pi^2-9)}$
And parapositronium
$t=\frac{h}{\pi m_ec^...
- 925
1
vote
0
answers
38
views
How would we integrating high energy part of a relativistic quantum field theory to get a non-relativistic theory?
Relativistic quantum field theory (RQFT) is a after spring of quantum theory and special relativity. A novel thing in RQFT is the existence of anti-particle. That is, consider a relativistic field $\...
- 21
2
votes
0
answers
110
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Canonically quantizing the charged scalar field with massive gauge boson
I have a specific confusion in canonically quantizing the theory of a complex scalar field $\Phi$ and a real vector field $V^\mu$, with a Lagrangian density:
\begin{align*}
\mathcal{L} = -(D_\mu \...
- 433
3
votes
3
answers
830
views
A problem with QED
I have a small problem with the understanding of QED.
The equations of motion in QED are
$\square A^\mu=e\bar{\psi}\gamma^\mu\psi$
$\left(i\gamma^\mu\partial_\mu-m\right)\psi=e\gamma^\mu A_\mu\psi$
If ...
- 925
4
votes
1
answer
310
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Equivalence of Maxwell and electric field operator in the Coulomb gauge (minimal and polar coupling)
In the field theory literature, we find the interaction Hamiltonian coupling a point particle with charge $e$ and mass $m$ to the electromagnetic field to be
$$
\hat{H}_\text{int}(t)
=
-
\frac{e}{m}
\...
- 543