Peskin & Schroeder QFT Born Approximation reference.

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Discussion Overview

The discussion revolves around the application of the Born approximation in quantum field theory (QFT) as presented in Peskin and Schroeder's "Introduction to QFT." Participants are exploring the relationship between the scattering amplitude and the transition operator, as well as seeking references for further reading on this topic.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant notes the use of the Born approximation in Peskin and Schroeder and seeks literature that explains the scattering amplitude in the form presented in their text.
  • Another participant claims that the expression relates to Fermi's Golden Rule, suggesting it is found in quantum mechanics textbooks that cover perturbation theory.
  • A different participant questions whether the expression is indeed Fermi's Golden Rule, pointing out that it typically involves the square of the matrix element and is not usually formulated in terms of the transition operator T.
  • Further discussion reveals that the S-matrix is related to the transition operator T, with a request for references that derive this relationship without using integral treatments.
  • One participant mentions that the scattering operator is related to the transfer operator and suggests that the derivation of the Born series can be found in standard quantum mechanics textbooks, specifically recommending J.J. Sakurai's "Modern Quantum Mechanics."
  • A participant expresses confusion regarding the relationship between the T operator and the S-matrix, referencing specific equations from Sakurai's text and noting that the S-matrix is not mentioned in the context they are studying.
  • Another participant discusses the Fourier transform of the non-relativistic matrix element and its implications for energy conservation in the context of the transition matrix.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the Born approximation, Fermi's Golden Rule, and the transition operator T. There is no consensus on the correct interpretation or the appropriate references for further reading.

Contextual Notes

Participants reference specific equations and concepts from quantum mechanics and QFT literature, indicating potential limitations in understanding the connections between these concepts. The discussion highlights the complexity of the relationships involved and the varying interpretations of foundational principles.

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I'm currently teaching myself some QFT trough Peskin and Schroeders Introduction to QFT and I've noticed that in several arguments they rely on appealing to the Born approximation of non-relativistic QM scattering theory. For example on page 121 equation (4.125) they appeal to the scattering amplitude

\langle p'|iT|p\rangle = -i \tilde{V}(\vec q) 2\pi \delta(E_\vec{p} - E_\vec{p'}).

I thought it might be a good idea to read up on this and I'm trying to find some literature where the scattering amplitude is stated in the form above and explained. I've had no success so far.

Does anyone have any good references?
 
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This is also known as "Fermi's Golden Rule". You find it in all textbooks on QM where perturbation theory (be it time-independent or time-dependent) is treated. You find the path-integral treatment in the first chapter of my QFT manuscript:

http://fias.uni-frankfurt.de/~hees/publ/lect.pdf
 
Is it really Fermi's golden rule?
There the square of \langle k'|V|k\rangle enters and I've never seen it being formulated in terms
of the transition operator T.
 
Indeed I saw the result in your manuscript formulated in terms of the S matrix. I've never seen Fermi's golden rule stated in that form. How is the S matrix related to T? Do you have any references where the same form is derived in a non integral treatment?
 
The scattering operator is related with the transfer operator by
\hat{S}=\hat{1}+\mathrm{i} \hat{T}.
You find the derivation of the Born series for the S- (or equivalently the T-)matrix in any good quantum mechanics textbook. For scattering theory, I'd recommend

J.J. Sakurai, Modern Quantum Mechanics, Addison Weseley.
 
I've read most of what seems relevant in J.J Sakurai (Revised Edition) , but I can't seem to make sense of that relation. How does the definition of the T operator

V|\Psi^{(+)}\rangle = T |\phi\rangle \ \ \ (7.2.16) \ \ \ page \ 389

correspond with the relation you stated

S = I + iT?

Furthermore by using equation (7.2.2) at page 386 togeather with eqn (7.2.19) at page 389 I get something like

\langle \vec k' |T |\vec k\rangle = \tilde{V}(\vec q).


J.J Sakurai does not even mention the S-matrix.
 
the non relativistic matrix element Fourier transform will correspond to a potential.the transition matrix contains a four delta function so one term which contains three delta function will give that potential and the left one will give contribution to energy conservation.
 

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