INFRARED FIXED POINT IN THE STRONG RUNNING COUPLING: UNRAVELING THE ΔI = 1/2 PUZZLE IN K-DECAYS

Abstract

In this paper, we present an explanation for the ΔI = 1/2 rule in K-decays based on the premise of an infrared fixed point α IR in the running coupling αs of quantum chromodynamics (QCD) for three light quarks u, d, s. At the fixed point, the quark condensate [Formula: see text] spontaneously breaks scale and chiral SU (3)L× SU (3)R symmetry. Consequently, the low-lying spectrum contains nine Nambu–Goldstone bosons: π, K, η and a QCD dilaton σ. We identify σ as the f0(500) resonance and construct a chiral-scale perturbation theory χPTσ for low-energy amplitudes expanded in αs about α IR . The ΔI = 1/2 rule emerges in the leading order of χPTσ through a σ-pole term KS→σ→ππ, with a gKSσ coupling fixed by data on γγ→π0π0 and KS→γγ. We also determine R IR ≈5 for the nonperturbative Drell–Yan ratio at α IR .