Shell-restricted scalar propagator
= Shell-restricted scalar propagator
{title2=$\widetilde C_>(p)=\mathbf1_{\Lambda^\prime<|p|\leq\Lambda}/(p^2+m^2)$}
The Gaussian contraction used while integrating out a momentum shell. Its Fourier support lies entirely in that shell. In particular, convolution with a purely low-momentum field is zero. This distinguishes shell <Feynman diagrams> from unrestricted loop diagrams.