Light sigma-Meson Production in Excited Upsilon Decay Processes II:   Theoretical Investigation
  The results of analyses obtained in Part I are examined from the viewpoint of chiral symmetry. The mass spectra of pi pi system are widely believed to be suppressed generally near the threshold, because of the derivative coupling property of Nambu-Goldstone pi meson. However, this suppression does not hold in the processes with large energy release, and the steep increase from the pi pi threshold observed in the transition Upsilon (3S-->1S) is shown to be consistent with general constraints from chiral symmetry. 
Muneyuki Ishida (TITech), Shin Ishida (Nihon U.) and Toshihiko Komada   (Nihon U.)