### Speaker

Rod Crewther
(University of Adelaide)

### Description

We observe that flavor current conservation constrains the structure of chiral-scale perturbation theory ChPT_sigma. This theory addresses the disagreement between experiment and lowest order chiral SU(3) x SU(3) perturbation theory (ChPT_3) for amplitudes involving the f_0(500) resonance and O(m_K) extrapolations in momenta. In ChPT_sigma, it is assumed that 3-flavor QCD has an infrared fixed point where the chiral condensate induces nine Nambu-Goldstone bosons: pi, K, eta and a QCD dilaton sigma which we identify with f_0(500). In the leading order of ChPT_sigma, dilaton-pole dominance explains the Delta I = 1/2 rule in nonleptonic K-decays. The effect of the simplification noted above is that the theory becomes more predictive for the decays sigma -> pi pi and sigma -> gamma gamma and hence for the sigma NN coupling.

### Primary author

Rod Crewther
(University of Adelaide)

### Co-author

Dr
LEWIS TUNSTALL
(UNIVERSITY OF BERN)