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I'm currently having fun with the Dirac matrices $\gamma^\mu$ which appear in the relativistic Fermion field equation (aka the Dirac equation). They need to satisfy the anticommutation relation $$ \{\gamma^\mu,\gamma^\nu\}=\gamma^\mu\gamma^\nu+\gamma^\nu\gamma^\mu=2\eta^{\mu\nu} $$ in order for the Dirac equation ($i\gamma^\mu\partial_\mu-m)\psi=0$ to provide the correct relativistic energy-momentum expression.

Famously, the $\gamma^\mu$ must be at least 4-dimensional matrices, in order to satisfy the required anticommutation relation. However, they are not unique. Indeed, if $\gamma^\mu$ is one possible 4x4 set, and V is a 4x4 invertible matrix, then $\gamma'^\mu = V\gamma^\mu V^{-1}$ is also a possible set (i.e. it too will satisfy the anticommutation relation). This is trivial to prove, since $V^{-1}V =1$.

Now I'm wondering if the converse is true: suppose I have two distinct sets of 4x4 matrices, $\gamma^\mu$ and $\gamma'^\mu$, which both satisfy the anticommutation requirement. Is it then true, that there exists an invertible 4x4 Matrix V, such that $\gamma'^\mu=V\gamma^\mu V^{-1}$? Is there a way to obtain an explicit expression for V in terms of $\gamma'^\mu$ and $\gamma^\mu$?

Qmechanic
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Yes, it's the content of Pauli's Lemma (1936). You can find a full answer here:

Choice of Dirac gamma matrix representation and definition of adjoint spinor and a proof of the lemma in Pauli's article:

Pauli,W. (1936), « Contributions mathématiques à la théorie des matrices de Dirac », in Annales de l'institut Henri Poincaré (Vol. 6, No. 2, pp. 109-136) (article freely available on the Numdam repository).

If you do not read French, then you can find an English proof in B. Thaller's "The Dirac Equation", Springer, 1992, p. 74.

DanielC
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