Observations on the Isostructure of Currents

Model-independent implications of the isostructure of currents for $\gamma -$, $e-$, $\nu -$, and $\overline{\nu }$-induced production reactions are noted. Reactions on hydrogen and deuterium only are considered; separate neutron information is not used. Numerous tests are given for the absence of $I=2\mathrm{}$ (or specific higher $I$ values), for the electromagnetic current, and for the weak $\Delta S=0\mathrm{}$ current (independent of class). Similar results are derived for the $\left|\Delta I\right|=\frac{1}{2}$ rule for $\left|\Delta S\right|=1\mathrm{}$ currents, where $\overline{\nu }-d$ reactions are most favorable. A consequence for $K_{14}$ decays is mentioned. The expansion of cross sections in terms of the azimuthal angle between the lepton and a hadron plane yields equalities implied by the absence of second-class currents (independent of isospin content) in $T$-conserving situations. Here the $\nu$ and $\overline{\nu }$ disintegrations of the deuteron are of special interest.