# Fermi theory

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1. May 18, 2015

### LupusLupus

Could you explain what's the interpretation of $$a$$ before $$\gamma^{5}$$ in this current:

$$J_{\alpha}=\bar{\psi_{e}}\gamma^{\alpha}\left(1-a\gamma^{5}\right)\psi_{\nu_{e}} +\bar{\psi_{\mu}}\gamma^{\alpha}\left(1-a\gamma^{5}\right)\psi_{\nu_{\mu}}$$?

And will this factor complicate calculations of decay rate of muon very much? I've seen that the standard form of current in the most popular books contains just $$1-\gamma^{5}$$.

2. May 18, 2015