Patterns and partners for chiral symmetry restoration

Abstract

We present and analyze a new set of Ward Identities which shed light on the distinction between different patterns of chiral symmetry restoration in QCD, namely O(4) vs O(4) x U(1)_A. The degeneracy of chiral partners for all scalar and pseudoscalar meson nonet members is studied through their corresponding correlators. Around chiral symmetry degeneration of O(4) partners, our analysis predicts that U(1)_A partners are also degenerated. Our analysis also leads to I = 1/2 scalar-pseudoscalar partner degeneration at exact chiral restoration and supports ideal mixing between the η- η' and the f₀(500)-f₀(980) mesons at O(4) x U(1)_A restoration, with a possible range where the pseudoscalar mixing vanishes if the two transitions are well separated. We test our results with lattice data and provide further relevant observables regarding chiral and U(1)_A restoration for future lattice and model analyses.