Exchange Current Corrections to Neutrino-Nucleus Scattering. I. Nuclear Matter

Relativistic exchange current corrections to the impulse approximation in low and intermediate energy neutrino--nucleus scattering are presented assuming non--vanishing strange quark form factors for constituent nucleons. Two--body exchange current operators which treat {\em all} $SU(3)$ vector and axial currents on an equal footing are constructed by generalizing the soft--pion dominance method of Chemtob and Rho. For charged current reactions, exchange current corrections can reduce the impulse approximation results by 5 to 10 \% depending on the nuclear density. A finite strange quark form factor may change the total cross section for neutral current scattering by 20\% while exchange current corrections are found to be sensitive to the nuclear density. Implications on the current LSND experiment to extract the strange quark axial form factor of the nucleon are discussed.