Meson structures from random phase approximation

The structures of mesons (π and ρ) are analysed within the random phase approximation (RPA). The hypothesis of partial conservation of the axial current (PCAC) is used to show that the π meson has large amplitudes of sea quark excitation. The relations between the meson structures and the vacuum quark condensate are obtain for π and ρ mesons, respectively, which is the well-known Gell-Mann–Oakes–Renner (GOR) relation for π meson.