Regarding interacting green's function, I found two different description:(adsbygoogle = window.adsbygoogle || []).push({});

1. usually in QFT:

[itex]<\Omega|T\{ABC\}|\Omega>=\lim\limits_{T \to \infty(1-i\epsilon)}\frac{<0|T\{A_IB_I U(-T,T)\}|0>}{<0|T\{U(-T,T)\}|0>}[/itex]

2. usually in quantum many body systems:

[itex]<\Omega|T\{ABC\}|\Omega>=\frac{<0|T\{A_IB_I S\}|0>}{<0|T\{S\}|0>}[/itex]

where interaction is switched off at ##T=\pm\infty## (adiabatic approximation)

Is there any connection between the two descriptions?

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# Relation between adiabatic approximation and imaginary time

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