The vertex factors in QCD penguin operators

Click For Summary
SUMMARY

The discussion centers on the presence of the (V+A) term in the context of QCD penguin operators, specifically in equations O5 and O6. The (V+A) term is essential for projecting out the right Weyl from a Dirac spinor, while the electroweak theory dictates that (V-A) factors are assigned to Dirac spinor-W boson vertices due to W's coupling to left Weyl spinors. The participants express confusion over the necessity of the (V+A) term in the penguin diagrams, indicating that its inclusion is crucial for constraining potential V+A interactions.

PREREQUISITES
  • Understanding of QCD (Quantum Chromodynamics) principles
  • Familiarity with electroweak theory and Feynman rules
  • Knowledge of Dirac spinors and Weyl spinors
  • Basic grasp of penguin diagrams in particle physics
NEXT STEPS
  • Research the role of (V+A) and (V-A) terms in particle interactions
  • Study the implications of penguin diagrams in flavor physics
  • Explore the constraints on V+A interactions in theoretical models
  • Examine the derivation and applications of Feynman rules in electroweak processes
USEFUL FOR

Particle physicists, theoretical physicists, and researchers focusing on QCD and electroweak interactions will benefit from this discussion.

Elmo
Messages
37
Reaction score
6
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
 
Physics news on Phys.org
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.
 
Reply
  • Like
Likes   Reactions: Elmo
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.
 

Attachments

  • Screenshot (53).png
    Screenshot (53).png
    51.5 KB · Views: 221
  • Screenshot (54).png
    Screenshot (54).png
    43.5 KB · Views: 222
  • Screenshot (55).png
    Screenshot (55).png
    40 KB · Views: 203
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.
 

Similar threads

Graduate Operator Product Expansion as shown in Schwartz
  • · Replies 4 ·
Replies
4
Views
2K
Graduate The Factorization Theorem in Particle Physics
  • · Replies 6 ·
Replies
6
Views
2K
Graduate How the g factor comes from QFT?
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad The standard model from loop quantum gravity via spinors octonions
  • · Replies 26 ·
Replies
26
Views
5K
Graduate What is the Role and Significance of Feynman Diagrams in Quantum Physics?
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Understanding the Use of Trace in QFT Lagrangian for Chiral Symmetry in QCD
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad Progress In Calculating The HLbL Contribution To Muon g-2
  • · Replies 0 ·
Replies
0
Views
2K
Graduate Shaposhnikov and Hossenfelder, Higgs and MOND
  • · Replies 9 ·
Replies
9
Views
4K
Graduate Conformal field theory: vertex operator
  • · Replies 11 ·
Replies
11
Views
3K
Graduate New properties of "standard model effective field theory"
  • · Replies 7 ·
Replies
7
Views
3K