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@JamalS I have tried to calculate it myself, though I am not sure of my conclusion. My guess is that it does not form a Lorentz scalar because the transformation uses the fact that $\gamma^{0} \gamma^{0} = 1$, but this is not the case for $\gamma^{5}$? EDIT: $\gamma^{5}$ does have this property - so it should be able to take the role of $\gamma^{0}$ and construct a Lorentz scalar right?
