Model for the Q2 dependence of polarized structure functions.

Abstract

We present an update of a phenomenological model for the spin-dependent structure functions ${\mathit{g}}_{1}$(x,${\mathit{Q}}^{2}$) of the proton and neutron. This model is based on a broken SU(6) wave function parametrized by the unpolarized structure functions. The two free parameters of the model are chosen to satisfy the Bjorken and Ellis-Jaffe sum rules. The model respects isospin symmetry and has zero strange sea polarization. Using new values for F/D from hyperon \ensuremath{\beta} decay the resulting ${\mathit{Q}}^{2}$-dependent asymmetries ${\mathit{A}}_{1}$ are in perfect agreement with the existing data. Therefore we do not see any evidence for a ``spin crisis.'' With two choices for ${\mathit{g}}_{2}$ the ${\mathit{Q}}^{2}$ dependence of ${\mathit{A}}_{1}$(x,${\mathit{Q}}^{2}$) and ${\mathit{A}}_{2}$(x,${\mathit{Q}}^{2}$) \ensuremath{\surd}${\mathit{Q}}^{2}$/M is predicted and shown to be small for both cases.