DiracMatrix[mu] denotes a Dirac gamma matrix with Lorentz index \mu.
DiracMatrix[mu , nu , ...] is a product of \gamma matrices with Lorentz indices mu , nu , ...
DiracMatrix[5] is \gamma ^5.
DiracMatrix[6] is (1 + \gamma^5)/2.
DiracMatrix[7] is (1 - \gamma^5)/2.
The shortcut DiracMatrix is deprecated, please use GA instead!
DiracMatrix[\[Mu]]\bar{\gamma }^{\mu }
This is how to enter the non-commutative product of two. The Mathematica Dot “.” is used as non-commutative multiplication operator.
DiracMatrix[\[Mu]] . DiracMatrix[\[Nu]]\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }
DiracMatrix[\[Alpha]] // StandardForm
(*DiracGamma[LorentzIndex[\[Alpha]]]*)DiracMatrix is scheduled for removal in the future versions of FeynCalc. The safe alternative is to use GA.
GA[\[Mu]]\bar{\gamma }^{\mu }
GAD[\[Mu]]\gamma ^{\mu }
FCI[GA[\[Mu]]] === DiracMatrix[\[Mu]]\text{True}
FCI[GAD[\[Mu]]] === DiracMatrix[\[Mu], Dimension -> D]\text{True}