The Rare Decays $\piee$, $\etaee$ and \etamumu$ in Chiral Perturbation   Theory
  We calculate the decay rates for $\piee$, $\etaee$ and $\etamumu$ in chiral perturbation theory. The linear combination of counterterms necessary to render these amplitudes finite is fixed by the recently measured branching fraction for $\etamumu$. We find $\Br(\piee ) = 7\pm 1\times 10^{-8}$ and $\Br(\etaee )=5\pm 1\times 10^{-9}$. 
Martin J. Savage, Michael Luke, and Mark B. Wise