 Centered four-point cumulant decomposition

ID: centered-four-point-cumulant-decomposition

For a normalized Minkowski source functional

Z = e^{iW}

C_{n} = i^{1 - n} δ^{n} W / δ J^{n}

and

G_{1234} = C_{1234} + C_{12} C_{34} + C_{13} C_{24} + C_{14} C_{23} .

Differentiating

e^{iW}

assigns the four labels to connected blocks. Blocks of size one vanish, leaving one block of four or one of the three pair partitions. Thus

G_{4} = i W_{4} - \sum W_{2} W_{2}

in this source convention.

// Target: perturbative-quantum-field-theory.bigb

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