FeynCalc manual (development version)

SUNFDeltaContract

SUNFDeltaContract[exp] substitutes for all SUNFDelta in exp SUNFDeltaContract, contracts the fundamental $\text{SU}(N)$ indices and resubstitutes SUNFDelta.SUNFDeltaContract[i, j] is the Kronecker-delta for $\text{SU}(N)$ in the fundamental representation with contraction properties. It wraps the head SUNFIndex around its arguments.

See also

Overview, SUNFDelta, SUNFIndex.

Examples

SUNFDelta[SUNFIndex[a], SUNFIndex[b]]^2 
 
SUNFDeltaContract[%]

$$\delta _{ab}^2$$

$$N$$