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Watson's theorem and electromagnetism in K -> pi pi decay

S. Gardner·Ulf-G. Meißner·G. Valencia
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Abstract

We consider what constraints unitarity and CPT invariance yield on the strong and electromagnetic phases entering K -> pi pi decay. In particular, we show that the relative size of the electromagnetically-induced changes in the I=0 and I=2 phase shifts in the two--pion final state do not depend on the explicit coupling to the pi^+ pi^- gamma channel. This demonstrates that Watson's theorem can be extended to include the presence of electromagnetism. We point out the consequences for the general structure of the K -> pi pi decay amplitudes in the presence of isospin violation.

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S. Gardner, Ulf-G. Meißner, G. Valencia. 2001-03-13. Watson's theorem and electromagnetism in K -> pi pi decay. https://doi.org/10.1016/s0370-2693(01)00428-2

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