Roles of Chiral Symmetry and the Sigma Meson in Hadron and Nuclear Physics(§1. Historical and General Topics,Possible Existence of the σ-Meson and Its Implications to Hadron Physics)

概要

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We first review the recent accumulating evidences of the existence of a scalar-isoscalar meson with the mass 500 to 800 MeV which may be identified with the sigma meson as the quantum fluctuation of the amplitude of the chiral order parameter <q^^-q>. We indicate that phase shift analyses which respect chiral symmetry (ChS ), analyticity and crossing symmetry of the scattering amplitude show the sigma meson pole in the s-channel as well as the ρ meson pole in the t-channel in the π-π scattering in the I = J = 0 channel. We emphasize that the existence of the σ resonance does not contradict with the success of the chiral perturbation theory; phenomenological difficulties with the renormalizable linear sigma model do not necessarily deny the validity of the linear representation of ChS of QCD as given by the NJL-like models which not only admit the σ resonance but also reproduce the coupling constants L_i and H_i appearing the nonlinear chiral lagrangian. We give some examples of the hadronic phenomena which are naturally accounted for with the σ meson. We show that the the σ meson as the amplitude fluctuation of the chiral order parameter may be more clearly identified than in free space in hot and/or dense matter, even in finite nuclei where partial restoration of ChS may be realized.
素粒子論グループ素粒子研究編集部の論文
2001-02-20