PauliEta[I] represents a two-component Pauli spinor
\eta, while PauliEta[-I]
stands for \eta^{\dagger }.
PauliEta[I]\eta
PauliEta[-I]\eta ^{\dagger }
PauliEta[-I] . SIS[p] . PauliXi[I]
% // ComplexConjugate\eta ^{\dagger }.\left(\bar{\sigma }\cdot \overline{p}\right).\xi
\xi ^{\dagger }.\left(\bar{\sigma }\cdot \overline{p}\right).\eta