  Ab initio calculations of the quasi-elastic electromagnetic and neutral-weak
response functions of 4He and 12C are carried out for the first time. They are
based on a realistic approach to nuclear dynamics, in which the strong
interactions are described by two- and three-nucleon potentials and the
electroweak interactions with external fields include one- and two-body terms.
The Green's function Monte Carlo method is used to calculate directly the
Laplace transforms of the response functions, and maximum-entropy techniques
are employed to invert the resulting imaginary-time correlation functions with
associated statistical errors. The theoretical results, confirmed by experiment
in the electromagnetic case, show that two-body currents generate excess
transverse strength from threshold to the quasi-elastic to the dip region and
beyond. These findings challenge the conventional picture of quasi-elastic
inclusive scattering as being largely dominated by single-nucleon knockout
processes.
