An. Ivanov et al., ON THE PROBLEM OF THE TAU[-PI-O-GAMMA-GAMMA DECAY IN CHIRAL PERTURBATION-THEORY AT THE QUARK LEVEL, Nuovo cimento della Società Italiana di Fisica. A. Nuclei, particles and fields, 107(8), 1994, pp. 1375-1382
The partial width of the decay eta --> pi0 gammagamma is calculated wi
thin the chiral perturbation theory at quark level [(CHPT)q] exploitin
g the linear realization of chiral U(3) x U(3) symmetry: GAMMA(eta -->
pi0 gammagamma)(CHPT)q = (0.24 +/- 0.05) eV. The result is not compar
ed with the experimental one GAMMA(eta --> pi0 gammagamma)exp = (0.85
+/- 0.19) eV. It is confirmed that despite the essential progress of t
he experimental research of the decay eta --> pi0 gammagamma the neces
sity of the remeasuring of GAMMA(eta --> pi0 gammagamma), said out by
Ebert and Volkov in 1979, is still valid.