Tuesday, December 2, 2014

quantum mechanics - Can one show that gamma5dagger=gamma5 directly from the anticommutation relations?


Is it possible to show that γ5=γ5, where γ5:=iγ0γ1γ2γ3,

using only the anticommutation relations between the γ matrices, {γμ,γν}=2ημν1,
and without using any specific representation of this algebra and a unitary invariance argument, as is usually done?



Answer



As the comments explained, you need to know a few properties of the γ matrices. First of all, from {γμ,γν}=2ημν14

you can infer that (depending on the metric but not on the representation of the dirac algebra!) in (+---) metric γ0 is hermitian (hint: look at the μ=0,ν=0 component of the above equation), while the γi (i=1,2,3) are anti-hermitian. (In -+++ metric, this would be interchanged). And this should allow you to solve the problem.


The hermicity properties can be condensed into γμ=γ0γμγ0

which just reproduces the above if you take the commutation properties into account.


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