Spinor[p, m, o] is the head of Dirac spinors. Which of the spinors u, v, \bar{u} or \bar{v} is understood, depends on the sign of the momentum argument p and the relative position of Spinor in the chain.
Spinor[Momentum[p], m] means \bar{u} if it stands at the beginning of the chain.
Spinor[Momentum[p], m] means u if it stands at the end of the chain.
Spinor[-Momentum[p], m] means \bar{v} if it stands at the beginning of the chain.
Spinor[-Momentum[p], m] means v if it stands at the end of the chain.
Spinors of fermions of mass m are normalized to have \bar{u} u=2 m and \bar{v} v=-2 m.
The optional argument o can be used for additional degrees of freedom. If no optional argument o is supplied, a 1 is substituted in.
Overview, FermionSpinSum, DiracSimplify, SpinorU, SpinorV, SpinorUBar, SpinorVBar, SpinorUBarD, SpinorUD, SpinorVD, SpinorVBarD.
Spinor[Momentum[p]]\varphi (\overline{p})
Spinor[Momentum[p], m]\varphi (\overline{p},m)
FeynCalc uses covariant normalization (as opposed to e.g. the normalization used in Bjorken & Drell).
Spinor[Momentum[p], m] . Spinor[Momentum[p], m] // DiracSimplify2 m
DiracSimplify[Spinor[-Momentum[p], m] . GS[p]]-m \left(\varphi (-\overline{p},m)\right)
Spinor[Momentum[p]] // StandardForm
(*Spinor[Momentum[p], 0, 1]*)ChangeDimension[Spinor[Momentum[p]], D] // StandardForm
(*Spinor[Momentum[p, D], 0, 1]*)Spinor[Momentum[p], m] // StandardForm
(*Spinor[Momentum[p], m, 1]*)SmallVariables are discarded by Spinor.
Spinor[Momentum[p], SmallVariable[m]] // StandardForm
(*Spinor[Momentum[p], 0, 1]*)