Origin of Generalized Adler-Weisberger Sum Rule for the Nucleon and $\Delta(1232)$

Abstract

We derive a relation for the axial-coupling constants of the nucleon and spin-3/2 baryons including the $\Delta(1232)$ with the use of an $SU(2)_R\times SU(2)_L$ invariant Lagrangian. Therein the nucleon belongs to the fundamental representation of the chiral group, while the spin-3/2 baryons belong to higher-dimensional representations $(1,\half)\oplus (\half,1)$. The resulting relation reproduces the one derived from the generalized Adler-Weisberger (GAW) sum rule for the forward $\pi N$ scattering. We clarify the origin of the GAW sum rule for the nucleon and $\Delta$ by taking into account both the group-theoretical aspects and the spontaneous breaking of chiral symmetry. It turns out that the GAW sum rule for the nucleon and $\Delta$ is a consequence of the existence of interactions involving a derivative-pion-field and spontaneous chiral symmetry breaking. This implies that the couplings between $N$ and $\Delta$ in the GAW sum rule vanish with the change of the chiral condensate towards chiral restoration.