What are the disconnected Feynman diagrams in QFT?

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Discussion Overview

The discussion revolves around the identification and understanding of disconnected Feynman diagrams in quantum field theory (QFT), specifically in the context of Srednicki's textbook. Participants explore how disconnected diagrams relate to connected diagrams and their contributions to calculations.

Discussion Character

  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant is seeking clarification on how to identify disconnected Feynman diagrams as presented in Srednicki's Figure 9.2.
  • Another participant references Eq. (9.12) as relevant to the discussion of disconnected diagrams.
  • A further response suggests that the contributions of disconnected graphs can be calculated by taking the product of the contributions from their connected components.

Areas of Agreement / Disagreement

The discussion does not reach a consensus on the specifics of disconnected diagrams, as participants are still exploring the topic and seeking clarification.

Contextual Notes

There may be limitations in understanding due to the reliance on specific equations and figures from Srednicki's book, which are not fully detailed in the discussion.

omephy
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I am learning QFT from Srednicki's book.
However, in Figure 9.2 Srednicki has given all connected diagrams with E=0 and V=4. Are there any way to know the disconnected diagrams? Can you tell me what they are.
 
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Sure, see Eq. (9.12).
 
Can you please explain this for me?
 
Not really much to explain. The point is, we only need to calculate the contributions for the connected graphs, because... Because any disconnected graph consists of one or more connected components, and we get its contribution just by taking the product of its pieces.
 

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