FeynCalc manual (development version)

PauliIndexDelta

PauliIndexDelta[PauliIndex[i], PauliIndex[j]] is the Kronecker-delta in the Pauli space with two explicit Pauli indices i and j.

See also

Overview, PauliChain, PCHN, PauliIndex, DIDelta, PauliChainJoin, PauliChainCombine, PauliChainExpand, PauliChainFactor.

Examples

PauliIndexDelta[PauliIndex[i], PauliIndex[j]]

δij\delta _{ij}

PauliIndexDelta[PauliIndex[i], PauliIndex[j]]^2 
 
PauliChainJoin[%] 
 
PauliChainJoin[%%, TraceOfOne -> D]

δij2\delta _{ij}^2

44

DD

PauliIndexDelta[PauliIndex[i], PauliIndex[j]] PauliIndexDelta[PauliIndex[j], PauliIndex[k]] 
 
PauliChainJoin[%]

δijδjk\delta _{ij} \delta _{jk}

δik\delta _{ik}

PauliChain[PauliEta[-I], PauliIndex[i0]] PIDelta[i0, i1] // FCI // PauliChainJoin

(η)i1\left(\eta ^{\dagger }\right){}_{\text{i1}}

PauliIndexDelta[PauliIndex[i2], PauliIndex[i3]] PauliIndexDelta[PauliIndex[i4], PauliIndex[i5]] PauliChain[PauliIndex[i7], PauliXi[I]] PauliChain[PauliEta[-I], PauliIndex[i0]] PauliChain[PauliSigma[CartesianIndex[a]], PauliIndex[i1], PauliIndex[i2]] PauliChain[PauliSigma[CartesianIndex[b]], PauliIndex[i5], PauliIndex[i6]] PauliChain[m + PauliSigma[CartesianMomentum[p]], PauliIndex[i3], PauliIndex[i4]] 
 
PauliChainJoin[%]

(ξ)i7(η)i0δi2  i3δi4  i5(σa)i1  i2(σb)i5  i6(σp+m)i3  i4(\xi )_{\text{i7}} \left(\eta ^{\dagger }\right){}_{\text{i0}} \delta _{\text{i2}\;\text{i3}} \delta _{\text{i4}\;\text{i5}} \left(\overline{\sigma }^a\right){}_{\text{i1}\;\text{i2}} \left(\overline{\sigma }^b\right){}_{\text{i5}\;\text{i6}} \left(\overline{\sigma }\cdot \overline{p}+m\right)_{\text{i3}\;\text{i4}}

(ξ)i7(η)i0(σa.(σp+m).σb)i1  i6(\xi )_{\text{i7}} \left(\eta ^{\dagger }\right){}_{\text{i0}} \left(\overline{\sigma }^a.\left(\overline{\sigma }\cdot \overline{p}+m\right).\overline{\sigma }^b\right){}_{\text{i1}\;\text{i6}}

PauliChainJoin[% PIDelta[i0, i1]]

(ξ)i7(η.σa.(σp+m).σb)i6(\xi )_{\text{i7}} \left(\eta ^{\dagger }.\overline{\sigma }^a.\left(\overline{\sigma }\cdot \overline{p}+m\right).\overline{\sigma }^b\right){}_{\text{i6}}

PauliChainJoin[% PIDelta[i7, i6]]

η.σa.(σp+m).σb.ξ\eta ^{\dagger }.\overline{\sigma }^a.\left(\overline{\sigma }\cdot \overline{p}+m\right).\overline{\sigma }^b.\xi