Deep-inelastic response of liquid helium

We calculate the deep-inelastic response of superfluid 4He and normal 3He. Following the Monte Carlo scheme of Carraro and Koonin, we represent the FSE by sampling the one-dimensional scattering wave function of the recoiling atom in a static background. We perform diffusion Monte Carlo simulations, using optimized trial functions and adopting the fixed node approximation for 3He. For 4He the agreement with recent high precision measurements is excellent, whereas in the case of 3He a small but not negligible discrepancy with available experimental information exists. Possible biases in the calculation are discussed, but the question remains open. This is not the first instance where some inconsistency is found between theoretical calculations and the analysis of neutron scattering data for 3He. We have also considered two very different fermion wave functions, yielding either a discontinuous or a continuous momentum distribution. They give hardly distinguishable results for the response, ruling out the possibility of detecting the discontinuity by deep-inelastic neutron scattering at the present level of experimental accuracy. (author)