Singlet GB contributions in the chiral constituent quark model
  The implications of the latest data pertaining to \bar u-\bar d asymmetry and the spin polarization functions on the contributions of singlet Goldstone boson \eta' within \chiCQM with configuration mixing for explaining the ``proton spin problem'' have been investigated. It is found that the present data favors smaller values of the coupling of singlet Goldstone Boson \eta' as compared to the corresponding contributions from \pi, K and \eta Goldstone bosons. It seems that a small non-zero value of the coupling of \eta' (\zeta \neq 0) is preferred over \zeta=0 phenomenologically. 
Harleen Dahiya, Manmohan Gupta and J.M.S. Rana