3
votes
0answers
37 views

What is the phase space for outgoing photons?

For a scattering process for which $n$ fermions are scattered, (by some conventions) the cross section acquires a phase space factor of: $$d\sigma \sim \prod_{i=1}^n\frac{d^3p_i}{(2\pi)^3 2E_i}$$ ...
1
vote
0answers
22 views

Physical interpretation of scalar tadpole loops

In Feynman diagrams, fermionic loops are drawn like this: While scalar loops are drawn as tadpoles: I assume the difference comes from the scalar not having an anti-particle. But how should one ...
2
votes
3answers
135 views

What's the difference between t-channel and s-channel in particle physics

As the Feynman diagram shows above. Does the s-channel and t-channel stands for exactly same reaction or they have big difference? Many thanks in advance enter image description here
3
votes
2answers
323 views

Higgs boson production via positron-electron collision

One of the suggested diagrams for the Higgs production is the following: so basically an electron-positron pair annihilates and forms an (excited?) Z boson, which then decays into another (less ...
-2
votes
3answers
183 views

What is the difference between these two Feynman diagrams?

In which direction is time flowing and what reactions do they represent? EDIT for Gigi (I could not add a comment to your answer): 1) Do Feynman diagrams by definition only show fundamental ...
3
votes
0answers
57 views

Feynman Toy Model Constraints on Number of Each Kind of External Lines

(From my homework) In our toy model we have three kinds of spinless particles: $A$, $B$, and $C$. The primitive vertex of decay/interaction is shown below: My actual problem statement says: ...
2
votes
1answer
293 views

Feynman diagram for pair production in matter

I'm aware that electron pair-production from a single photon requires the presence of matter — say some large nucleus — able to absorb momentum, as in the process \begin{align} N \gamma \rightarrow N ...
0
votes
1answer
101 views

Little confusion in drawing Feynmam diagram

If the arrows of both the outgoing solid lines of the Feynman diagram corresponding to the bhabha scattering of $e^+$ and $e^-$, are just reversed, will it not describe same thing? Doesn't both imply ...
2
votes
1answer
111 views

What is the difference between QFT and elementary particle physics?

I'm a little unclear as to how QFT differs from Elementary particle physics. They both use pictorials of Feynman graphs, is it that Elementary particle physics assumes the point particle perspective, ...
2
votes
1answer
106 views

No valid Feynman diagram for processes

This will likely be easy for anyone experienced in particle physics, but I'm not. I'm asked to explain why it is impossible to construct a valid Feynman diagram using Standard Model vertices for the ...
0
votes
1answer
96 views

Why do arrows point backwards in time for Feynman Diagrams?

I've been looking into Feynman Diagram for quite some time, and the fact that anti-particles point backwards in time after an interaction has been puzzling me. I understand this to be some convention ...
2
votes
0answers
91 views

Møller scattering: twisted?

I am studying the Møller scattering, but I don't know how to get the twisted diagram from the S-matrix. Has anybody a good explanation?
3
votes
1answer
214 views

Electron-Positron Scattering using the Feynman Rules - Integration Q

I'm doing independent studies on electron-positron scattering, specifically the annihilation diagram contribution to the M matrix in Bhabha scattering, and this is the equation I recovered with the ...
0
votes
0answers
56 views

Reduced graphs and pinch-singular surfaces

I am reading a book on perturbative QCD by John Collins. In Chapter 5, the terms reduced graph and pinch-singular surface are used for the analysis of mass singularities. However, their meanings are ...
2
votes
1answer
182 views

Feynman diagram for $\overline{K}\,\!^0$ antimeson production on the quark-level

I've recently stumbled upon a physics problem concerning $\overline{K}\,\!^0$ antimeson production. In this particular example, colliding a $\pi^-$ meson with a stationary proton yields a $K^0$ meson ...
4
votes
0answers
57 views

Helicity dependence in loop diagrams

I am trying to evaluate a diagram that looks like The middle of the diagram is a fermion loop. I know that the coupling between the $Z^0$ and fermions depends on the fermions' helicities, so it ...
2
votes
2answers
303 views

Feynman diagrams in three dimensions

Is there such a thing as an extension of Feynman diagrams into three dimensions? Canonical Feynman diagrams use one space and one time dimension to visualize processes involving elementary particles ...
2
votes
0answers
77 views

Chirality when moving around legs in Feynman diagrams

Assuming one has the following term in a Lagrangian: $$ g (\overline{A_R} B_L)(\overline{C_R}D_L) $$ where A,B,C,D correspond to spin 1/2 Dirac particles and the subscripts $R$ and $L$ denote left- ...
6
votes
3answers
276 views

Is there a simple way to compute some physical constant from Feynman diagram statistics?

I've been playing around writing some software to generate Feynman diagrams for QED, respecting the vertex "rules" described here, and avoiding creating isomorphic duplicates. So from a starter ...
6
votes
1answer
233 views

SUSY, ways to boost Chargino/Neutralino production?

Does anybody know a good reference that works out the equations for the Chargino/Neutralino production cross section in SUSY? I'm trying to understand if there are any tricks for boosting the ...
2
votes
1answer
260 views

4th order feynman-diagrams for $e^- + \mu^+ \to \nu_e + \bar{\nu}_\mu$

The task is to draw the two 4th-order Feynman diagrams of: $$e^- + \mu^+ \to \nu_e + \bar{\nu}_\mu $$ I drew the first one as (time left->right): ...
6
votes
2answers
824 views

How do we distinguish between virtual particle exchange and particle decay?

The difference between virtual particles and unstable particles is discussed at length in this question (namely, virtual particles correspond to internal lines in Feynman diagrams and are not ...
0
votes
1answer
136 views

weak bosons and feynman-stueckelberg interpretation

from Wiki "The W bosons have a positive and negative electric charge of 1 elementary charge respectively and are each other's antiparticle." Q:If each is the other's antiparticle then which is ...