The vertex factors in QCD penguin operators

In summary, (V+A) is included in Eqtns(5.4) as part of the projection operator for the right Weyl from a Dirac spinor. According to the Feynman rules of electroweak theory, there is a (V-A) assigned to each (Dirac) spinor-W boson vertex, but in penguin diagrams with a quark-antiquark loop coupling to the W, both vertices may have the same (V-A) factor. However, if the goal is to put constraints on a potential V+A interaction or component, it is necessary for it to be included.
  • #1
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TL;DR Summary
Not sure why there is a (V+A) term in here.
Have a look at O5 & O6 in Eqtns(5.4) . Why is there a (V+A) ?
(V+A) contains the projection operator which projects out the right Weyl from a Dirac spinor.
As per the Feynman rules of electroweak theory, there is a (V-A) assigned to each (Dirac) spinor-W boson vertex because W only couple to left Weyl spinors.
In the corresponding penguin diagrams there is the quark-antiquark loop coupling to the W so shouldn't both vertices have the same (V-A) factor always ?
Screenshot (51).png
 
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  • #2
Elmo said:
Summary:: Not sure why there is a (V+A) term in here.

so shouldn't both vertices have the same (V-A) factor always ?

Maybe. You didn't post enough for us to see what is being calculated. We therefore can't tell what should or should not be there.
 
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  • #3
Vanadium 50 said:
Maybe. You didn't post enough for us to see what is being calculated. We therefore can't tell what should or should not be there.
oh sorry.np Here it is.
 

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  • #4
You still haven't shown us what is being calculated. Why this slow drip...drip..drip of information?

If the goal is, for example, to put constraints on a potential V+A interaction or component, of course it needs to be there.
 
  • #5
Vanadium 50 said:
You still haven't shown us what is being calculated. Why this slow drip...drip..drip of information?

If the goal is, for example, to put constraints on a potential V+A interaction or component, of course it needs to be there.
oh actually no,I think its all clear now.
Sorry for bugging ye all.
Thanks anyway.
 

1. What are vertex factors in QCD penguin operators?

Vertex factors in QCD penguin operators are coefficients that describe the interaction strength between two quarks and a gluon. They play a crucial role in calculating the amplitudes of penguin diagrams in quantum chromodynamics (QCD).

2. How are vertex factors calculated?

Vertex factors are calculated using perturbative methods in QCD. This involves using Feynman diagrams to represent the interactions between quarks and gluons, and then applying mathematical techniques to calculate the amplitudes of these diagrams.

3. What is the significance of vertex factors in QCD penguin operators?

Vertex factors are important because they determine the strength of the strong interaction between quarks and gluons. This is crucial for understanding the behavior of particles in high-energy physics experiments, as well as for making accurate predictions about their properties.

4. How do vertex factors affect penguin diagrams in QCD?

Vertex factors play a crucial role in penguin diagrams in QCD. They determine the overall strength of the penguin interaction, and can also affect the direction and magnitude of the resulting amplitude. Without vertex factors, penguin diagrams would not accurately represent the behavior of particles in QCD.

5. Can vertex factors be experimentally measured?

No, vertex factors cannot be directly measured in experiments. They are theoretical quantities that are calculated using perturbative methods in QCD. However, the predictions made using these calculations can be tested experimentally, providing indirect evidence for the existence and accuracy of vertex factors.

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