Understanding Renormalization in Quantum Field Theory

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Discussion Overview

The discussion revolves around the concept of renormalization in quantum field theory, specifically focusing on the behavior of the renormalized coupling constant as a cutoff parameter approaches infinity. Participants explore mathematical expressions related to this topic, referencing specific formulas from a textbook.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses confusion regarding the introduction of a cutoff, M, in the context of the photon propagator and its implications for the renormalized coupling constant as M approaches infinity.
  • Another participant questions whether the renormalized charge, e_R, tends to infinity when M^2 goes to infinity, referencing a specific formula from Halzen and Martin.
  • A participant attempts to clarify the mathematical behavior of logarithmic functions as their arguments approach infinity, stating that the limit of log(x²) is not zero.
  • There is a discussion about the correct interpretation of logarithmic limits, with one participant suggesting that log(x) approaches infinity as x approaches infinity.
  • A later reply acknowledges a misunderstanding regarding the logarithmic limit and reflects on the need to recheck previous work due to a feverish state affecting clarity.

Areas of Agreement / Disagreement

Participants express differing views on the behavior of the renormalized charge and the limits of logarithmic functions, indicating that there is no consensus on these mathematical interpretations.

Contextual Notes

Some participants exhibit uncertainty about the mathematical steps involved in the renormalization process and the implications of the cutoff parameter, suggesting that further clarification may be needed.

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When was reading about renormalization I did no understand the main Idea of the last :(:confused:
It has been considered photon propagator with virtual pair of electron/pozitron. Takeing that loop integral the M^2 cuttoff is introduced, which tends then to ininifity, M^2 is "sopped up" in renormalized coupling constant, but even then when M^2 tends to infinity the coupling constant runs to infinity? Yes? Am I clear?

Pls help
 
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One help needed please

Gents,
I am not familiar with physics and that's why my questions may seem stupid for you, but could you pls help me and explain the Idea of formula 7.27 in attached file from Halzen F., Martin A.D. Quarks and leptons.
Does not the e_R tends to infinity when M^2 goes to infinity?
Thank you very much.
 

Attachments

Norman said:
No,
\lim_{x\rightarrow\infty} Log[x^2]=0
So,
\lim_{x\rightarrow\infty} 1-Log[x^2]=1
So it does not go to infinity as M goes to infinity.

? :confused:
 
vanesch said:
? :confused:

My feelings exactly!

Regards,
George
 
Sorry, in my sickly, feverish state I didn't elaborate. He is asking about how Halzen and Martin go about doing renormalization of the electric charge. They introduce the cut-off, M, and show that the renormalized charge goes like:
e_r \approx e(1-Log[M^2])^{\frac{1}{2}}
With a bunch of stuff I cannot remember off hand. So my understanding of the question was basically a simple math question. What does the limit as M-> infty do to e_r.
Did I misinterperet or just not state enough in my original post? Maybe my math is completely wrong, that tends to happen with a fever...
 
Last edited:
The limit of log(x²) as x->infin isn't zero.
 
isn't it 2 \log x and \log x approaches to infinity at x->\infty?
 
OMG...:smile: :smile:
Well, the good news is I am feeling better and now see where I went wrong... :blushing: :blushing: :blushing: I even checked it with mathematica, funny thing is if you switch the variable and the base in mathematica, you get a very different answer...

time to get some rest... I suppose this means all the work I did today needs to be rechecked. :biggrin:

Edit: I deleted the post- my shame is too deep...
 
Last edited:

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