# Neutral pion decay

by physguy09
Tags: decay, neutral, pion
 P: 19 So I know the neutral pion decays as $$\pi \rightarrow \gamma\gamma$$ my question is though, what forbids this from being an electromagnetic decay? I know it is not decaying via the strong force as there are no quarks resulting from decay. However, I do not see what forbids this from decaying via the EM force, if it is spitting out two gammas, which is the EM force carrier. Parity, G-parity, and Energy are conserved, as well as strangeness and angular momentum, so, what exactly forbids this from being EM?
 P: 23 What makes you think it isn't an electromagnetic decay? I would say that it is.
 PF Gold P: 2,883 EM it is, but anomaly.
P: 1,136

## Neutral pion decay

It's not forbidden but it would be under conservation of
the axial current density $j_A^\mu$. (The latter is only conserved
together with the Chern Simons current of the EM field)

Regards, Hans

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