Gamma-matrix trace
= Gamma-matrix trace
A gamma-matrix trace is a <matrix trace> of products of <gamma matrix>[gamma matrices]. In four spacetime dimensions, $\operatorname{tr}(\gamma^\mu\gamma^\nu)=4\eta^{\mu\nu}$ and $\operatorname{tr}(\gamma^\mu\gamma^\nu\gamma^\rho\gamma^\sigma)=4(\eta^{\mu\nu}\eta^{\rho\sigma}-\eta^{\mu\rho}\eta^{\nu\sigma}+\eta^{\mu\sigma}\eta^{\nu\rho})$.