Neutral Pion Decay: What Forbids EM Force?

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SUMMARY

The neutral pion decays via the process \(\pi \rightarrow \gamma\gamma\), but this decay is not classified as electromagnetic (EM) due to the conservation laws governing axial current density. While parity, G-parity, energy, strangeness, and angular momentum are conserved, the decay is prohibited under the conservation of the axial current density \(j_A^\mu\). This indicates that although the decay produces two gamma photons, it does not qualify as an EM decay due to the anomaly associated with the axial current.

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physguy09
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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?
 
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What makes you think it isn't an electromagnetic decay?

I would say that it is.
 
EM it is, but anomaly.
 
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
 
Last edited:

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