Effects of light scalar mesons in η→3π decay

We study the role of a possible nonet of light scalar mesons in the still interesting η→3π decay process, with the primary motivation of learning more about the scalars themselves. The framework is a conventional nonlinear chiral Lagrangian of pseudoscalars and vectors, extended to include the scalars. The parameters involving the scalars were previously obtained to fit the s-wave ππ and πK scatterings in the region up to about 1 GeV as well as the strong decay η′-ηππ. At first, one might expect a large enhancement from diagrams including a light σ(560). However there is an amusing cancellation mechanism which prevents this from occurring. In the simplest model there is an enhancement of about 13 percent in the η→3π decay rate due to the scalars. In a more complicated model which includes derivative type symmetry breakers, the cancellation is modified and the scalars contribute about 30 percent of the total decay rate (although the total is not significantly changed). The vectors do not contribute much. Our model produces a reasonable estimate for the related a₀(980) - f₀(980) mixing strength, which has been a topic of current interest. Promising directions for future work along the present line are suggested.