The vertex factors in QCD penguin operators

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Discussion Overview

The discussion revolves around the presence of the (V+A) term in the context of QCD penguin operators, specifically in relation to the Feynman rules of electroweak theory and the coupling of Dirac spinors to W bosons. Participants explore the implications of this term and its relationship to the (V-A) factors typically associated with left Weyl spinors.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the inclusion of the (V+A) term in the context of penguin diagrams, suggesting that both vertices should consistently exhibit a (V-A) factor due to the coupling of W bosons to left Weyl spinors.
  • Another participant expresses uncertainty about the calculations being performed, indicating that insufficient information has been provided to assess the situation.
  • A later reply emphasizes the need for clarity regarding the calculations, suggesting that if the goal is to impose constraints on a potential V+A interaction, then the term must be present.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the necessity or implications of the (V+A) term, with ongoing questions about the calculations and their context. Multiple views regarding the appropriateness of the (V+A) versus (V-A) factors remain unresolved.

Contextual Notes

The discussion lacks detailed information about the specific calculations being referenced, which may affect the understanding of the role of the (V+A) term. There are also indications of assumptions regarding the nature of the interactions being analyzed.

Elmo
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TL;DR
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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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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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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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.
 
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.
 

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