GA[mu]
can be used as input for a 4-dimensional \gamma^{\mu } and is transformed into
DiracGamma[LorentzIndex[mu]]
by FeynCalcInternal
(=FCI).
GA[mu , nu , ...]
is a short form for
GA[mu].GA[nu]
.
Overview, DiracGamma, GAD, GS.
[\[Mu]] GA
\bar{\gamma }^{\mu }
[\[Mu], \[Nu]] - GA[\[Nu], \[Mu]] GA
\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }-\bar{\gamma }^{\nu }.\bar{\gamma }^{\mu }
StandardForm[FCI[GA[\[Mu]]]]
(*DiracGamma[LorentzIndex[\[Mu]]]*)
[\[Mu], \[Nu], \[Rho], \[Sigma]] GA
\bar{\gamma }^{\mu }.\bar{\gamma }^{\nu }.\bar{\gamma }^{\rho }.\bar{\gamma }^{\sigma }
StandardForm[GA[\[Mu], \[Nu], \[Rho], \[Sigma]]]
(*GA[\[Mu]] . GA[\[Nu]] . GA[\[Rho]] . GA[\[Sigma]]*)
[\[Alpha]] . (GS[p] + m) . GA[\[Beta]] GA
\bar{\gamma }^{\alpha }.\left(\bar{\gamma }\cdot \overline{p}+m\right).\bar{\gamma }^{\beta }