All Questions
37
questions
0
votes
1
answer
52
views
Square of the Feynman amplitude for $a +b\to c+d$ and its reverse
In quantum field theory, if a process $a +b\to c+d$ is allowed by a certain interaction Lagrangian (hermitian), the reverse process, $c+d\to a+b$, must also be allowed (as far as I understand) by the ...
- 11.8k
0
votes
0
answers
73
views
Mandelstam variables sign
I am self-studying the book "Quantum Field Theory and the Standard Model" by Schwartz, on page 99 (paragraph "Mandelstam variables"), the context is the $2\rightarrow 2$ scattering ...
- 613
1
vote
0
answers
83
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Doubt in $e^{+}e^{-}\rightarrow W^{+}W^{-}$ scattering
I am trying to understand how to compute the scattering amplitude for the process $e^{+}e^{-}\rightarrow W^{+}W^{-}$, as a reference one could look at Peskin chapter 21.
What I do not understand is ...
- 475
13
votes
1
answer
2k
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How does one describe individual particles in QFT in practice?
A similar question was posted on this site at least ten times, but not quite in this formulation, and with no satisfactory answers, so I give it another try.
Quantum field theory textbooks almost ...
- 290
1
vote
1
answer
72
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Inconsistency in the $2\to 2$ kinematics
I must be confusing something horribly, because this should be very simple, but I am keep getting inconsistent results in the basic 2->2 scattering kinematics.
Let the process be $$a(p_1) + b(p_2) \...
- 857
1
vote
0
answers
49
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Relation between matrix element of a process with its crossed processes
Consider a process in particle physics denoted by, $$(1) \quad a+b\to c+d$$ which is related to the reverse process $$(2)\quad c+d\to a+b.$$ By virtue of the hermiticity of the interaction Hamiltonian,...
- 11.8k
4
votes
1
answer
117
views
$γγh$ interaction in the Standard Model
The topology for the lowest order $γγh$ interaction in the Standard Model is given by
where we have an intermediate top quark loop. I am confused with the charge conservation at each vertex. Since ...
- 1,783
2
votes
2
answers
177
views
How can QFT perturbation be used for electron-positron scattering?
I'm studying scattering and perturbation theory in QFT from Peskin and Schroeder book. After all the calculations and theory developing, they made a calculation for $$e^-e^+\to\mu^-\mu^+$$ scattering. ...
- 97
1
vote
1
answer
189
views
$\nu_e \bar{\nu_e} \rightarrow e^- e^+$ confusion
Interacting part of the $SU(2)_L$describing the Higgs and fermionic sector with one family
$$\mathcal{L}= \bar{l}_Li\not Dl_L+\bar{e}_Ri\not\partial e_R+ \bar{\nu}_Ri\not\partial\nu_R - (y_{\nu}\bar{l}...
- 3,464
6
votes
2
answers
574
views
What is string theory's replacement of interaction terms from Quantum field theory?
In Quantum Field Theory, the calculation of scattering amplitudes relies on interaction terms like $\lambda \phi^4$ or $\psi ' \gamma ^{\mu} \psi$. These are products of field operators calculated at ...
- 6,355
1
vote
1
answer
101
views
Muon pair production
Does muon pair production ($e^+ + e^- \rightarrow \mu^+ + \mu^-$) not have a $t$-channel at the lowest order (at the tree level)? All sources like Schwartz, etc. seem to only solve for $s$-channel, ...
- 433
1
vote
0
answers
147
views
LSZ reduction formula relation
LSZ formula gives a relation between the scattering amplitudes and correlators as
$$\langle f |i \rangle = (-i)^{m+n}\int \Pi_{i=1}^m d^4x_, e^{ik_i'x_i (\Box_{x_i} -m^2)}\Pi_{j=1}^n d^4x_, e^{ik_j ...
- 3,464
4
votes
1
answer
338
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What is the physical interpretation of the two tree-level Feynman diagrams for $e^-e^- \to e^-e^-$ scattering?
In the tree level, the $e^-e^- \to e^-e^-$ scattering has two Feynman diagrams, the first one is indicative that one electron emitted a photon which was later absorbed by the other electron:
However,...
- 43
1
vote
1
answer
368
views
Deep inelastic scattering (DIS) and handbag diagram
Here, in page 11, you can see the so-called 'handbag' diagram that explains how a virtual photon emitted in a deep inelastic scattering (DIS) process interacts with a parton.
I'm going to use this ...
- 1,597
0
votes
0
answers
99
views
Deep inelastic electron-proton scattering amplitude
In 'QCD and collider Physics' book by Ellis, Stirling and Webber, chapter 4.2 'The parton model from field theory' there is this equation for the amplitude of the process $e^- (k) P \rightarrow e^- (k^...
- 1,597