Linear realization of SU(3) parity doublet model for octet baryons with bad diquark

Abstract

We construct a linear $SU(3)_L \times SU(3)_R$ parity doublet model for octet baryons. Our model employs the $(3,\bar{3}) + (\bar{3},3)$ and $(3,6) + (6,3)$ chiral representations while excluding the $(8,1) + (1,8)$ representation. Through systematic analysis, we demonstrate that the $(3,6) + (6,3)$ representation containing symmetric ``bad'' diquarks, despite being energetically disfavored, is essential for reproducing the correct baryon mass hierarchy, particularly the $Σ$$Ξ$ mass ordering. The model incorporates both spontaneous and explicit chiral symmetry breaking, with the latter implemented through bare quark mass terms that properly account for $SU(3)$ flavor breaking effects. Our numerical analysis successfully reproduces the ground-state octet baryon masses and predicts the spectrum of excited states up to 2.5 GeV. For the experimentally challenging $Ξ$ sector, we provide specific predictions for spin-parity assignments: identifying $Ξ(1950)$ as the first positive-parity excitation. The analysis reveals that ground states are dominated by the $(3,\bar{3}) + (\bar{3},3)$ representation, consistent with the preference for ``good'' diquark configurations, while the $(3,6) + (6,3)$ contribution remains crucial for the mass spectrum.