When I am reading about the Wilson approach to renormalization in Chapter12.1 of Peskin & Shroeder I am wondering why are you allowed only to contract the [itex]\hat{\phi}[/itex] field (this is the field that carries the high-momentums degrees of freedom)as they show in equation 12.10, I thought that we should add all the contractions, between all the 4 fields and here is the term they are making the example of:(adsbygoogle = window.adsbygoogle || []).push({});

[itex]\int \mathcal{D}\hat{\phi}exp\left(-\int d^{d}x \frac{\lambda}{4}\phi^{2}\hat{\phi}^{2}\right)[/itex]

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# The renormalization group

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