ABSTRACT
We use recently derived Ward identities and lattice data for the light- and strange-quark condensates to reconstruct the scalar and pseudoscalar susceptibilities ( χ S κ , χ P K ) in the isospin 1/2 channel. We show that χ S κ develops a maximum above the QCD chiral transition, after which it degenerates with χ P K . We also obtain χ S κ within Unitarized Chiral Perturbation Theory (UChPT) at finite temperature, when it is saturated with the K 0 ∗ ( 700 ) (or κ ) meson, the dominant lowest-energy state in the isospin 1/2 scalar channel of π K scattering. Such UChPT result reproduces the expected peak structure, revealing the importance of thermal interactions, and makes it possible to examine the χ S κ dependence on the light- and strange-quark masses. A consistent picture emerges controlled by the m l / m s ratio that allows one studying K - κ degeneration in the chiral, two-flavor and SU(3) limits. These results provide an alternative sign for O ( 4 ) × U ( 1 ) A restoration that can be explored in lattice simulations and highlight the role of strangeness, which regulated by the strange-quark condensate helps to reconcile the current tension among lattice results regarding U ( 1 ) A restoration.
