Effect of light scalar mesons in η → 3π

We discuss the decay η → 3π, for which the observed branching ratio is larger than the simplest predict ions from chiral symmetry. This process occurs primarily due to strong isospin violation and so is in principle a sensitive measure of the up-down quark mass difference. We study the role of a possible nonet of light scalar mesons in the η → 3π decay. Using a non-linear chiral Lagrangian approach which successfully describes several other strong processes, we find that the inclusion of the scalar mesons leads to a modest increase relative to the simplest prediction. The main effect of the scalar mesons is due to a light broad σ meson