DEEP-INELASTIC RESPONSE OF LIQUID-HELIUM

We calculate the deep-inelastic response of superfluid He-4 and normal He-3. Following the Monte Carlo scheme of Carraro and Koonin, we repr esent the final-state effects by sampling the one-dimensional scatteri ng wave function of the recoiling atom in a static background. We perf orm diffusion Monte Carlo simulations, using optimized trial functions and adopting the fixed node approximation for He-3. For He-4 the agre ement with recent high-precision measurements is excellent, whereas in the case of He-3 a small but not negligible discrepancy with availabl e experimental information exists. Possible biases in the calculation are discussed, but the question remains open. This is not the first in stance where some inconsistency is found between theoretical calculati ons and the analysis of neutron-scattering data for He-3. We have also considered two very different fermion wave functions, yielding either a discontinuous or a continuous momentum distribution. They give hard ly distinguishable results for the response, ruling out the possibilit y of detecting the discontinuity by deep-inelastic neutron scattering at the present level of experimental accuracy. [S0163-1829(98)08038-2] .