The rare decay $\eta\to\pi\pi\gamma\gamma$ in chiral perturbation theory
  We investigate the rare radiative eta decay modes $\eta\to\pi^+\pi^-\gamma\gamma$ and $\eta\to\pi^0\pi^0\gamma\gamma$ within the framework of chiral perturbation theory at $O(p^4)$. We present photon spectra and partial decay rates for both processes as well as a Dalitz contour plot for the charged decay. 
G. Kn"ochlein, S. Scherer, D. Drechsel (Inst. f. Kernphysik,   University of Mainz, Germany)