The role of chiral loops in $\eta \to {\pi }^0{\pi }^0\gamma \gamma$

Abstract

We consider the rare decay $\eta \to {\pi }^0{\pi }^0\gamma \gamma$ and calculate the non-resonant contribution to the amplitude to one loop in Chiral Perturbation Theory. We display our result as both a diphoton energy spectrum and a partial decay rate as a function of the photon energy cut. It turns out that the one-loop correction can be numerically very important and could be detected, at sufficiently large center-of-mass photon energies, from a measurement of the partial decay width.

Comments: 10 pages, Latex. Discussion on the resonant background enlarged, sign error corrected, basic results unchanged. To appear in Phys. Lett. B