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## Homework Statement

I’m trying to learn Feynman diagrams from Peskin and Schroeder. I’m stuck right now on page 91-93, especially about constant factors and symmetry factors. Equation 4.44 and the two constants 3 and 12 in it make perfect sense to me. The trouble starts with 4.45. I understand it is one possible contraction from 10368 that all give the same expression.

Why the 1/3! in 4.45?

To get similar result for 4.45 as for 4.44, we need to replace the 1/3! With 10368 and add other expressions each with an overall constants. Correct?

On page 93 they say (first paragraph, second to last line) adding at each vertex this integral times minus I times game gives the overall constant. How on Earth does that give 10368?

*What*constant is

*why*by a symmetry constant 8 to large?

## Homework Equations

Peskin p.91-93

## The Attempt at a Solution

see above