In the study of Dirac fields in quantum field theory, Richard Feynman invented the convenient Feynman slash notation (less commonly known as the Dirac slash notation). If A is a covariant vector (i.e., a 1-form),
Using the anticommutators of the gamma matrices, one can show that for any and ,
where is the identity matrix in four dimensions.
- is the Levi-Civita symbol.
as well as the definition of four-momentum,
we see explicitly that
Similar results hold in other bases, such as the Weyl basis.