EXCITATION SPECTRUM OF A HE-3 IMPURITY IN SUPERFLUID HE-4

We present a variational Monte Carlo calculation of the excitation spe ctrum of one He-3 impurity in superfluid He-4 over the full momentum r ange. It includes backflow effects to high order. This is achieved wit h a shadow wave function in which the phase factors of the excitation are introduced in the subsidiary variables. Energy, effective mass and strength of the single excitation peak of the impurity are computed. Above q similar or equal to 0.5 Angstrom(-1) the effective mass increa ses significantly with q in agreement with experiment. No roton like m inimum is found and the impurity excitation brand crosses the phonon-r oton spectrum at q similar or equal to 1.6 Angstrom(-1).