Neutral Pion Decay: What Forbids EM Force?

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Discussion Overview

The discussion centers on the decay of the neutral pion into two gamma photons and explores the question of whether this process can be classified as an electromagnetic decay. Participants examine the forces involved and the conservation laws that apply to this decay process.

Discussion Character

  • Debate/contested

Main Points Raised

  • One participant notes that the neutral pion decays into two gamma photons and questions what forbids this from being an electromagnetic decay, given that parity, G-parity, energy, strangeness, and angular momentum are conserved.
  • Another participant asserts that the decay is indeed an electromagnetic decay.
  • A different viewpoint suggests that while it is an electromagnetic decay, it involves an anomaly.
  • Another participant argues that the decay is not forbidden but is constrained by the conservation of the axial current density, which must be considered alongside the Chern-Simons current of the electromagnetic field.

Areas of Agreement / Disagreement

Participants express differing opinions on whether the decay can be classified as electromagnetic. Some assert it is, while others highlight constraints that complicate this classification, indicating a lack of consensus.

Contextual Notes

Participants reference various conservation laws and theoretical constructs, such as axial current density and anomalies, but do not resolve the implications of these factors on the classification of the decay.

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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