Effect of roton backflow on quantum evaporation from superfluid He-4

We investigate the effect of roton backflow on the scattering of atoms, rot ons, and phonons at the free surface of superfluid He-4 at T = 0 K by inclu ding backflow semiphenomenologically in the form of a backflow potential in the theory of Sobnack, Inkson, and Fung [M. B. Sobnack, J. C. lnkson, and J. C. H. Fung, Phys. Rev. B 60, 3465 (1999)]. We assume that all the surfac e scattering processes are elastic and that the quasiparticles and atoms ar e incident with fixed parallel momenta to the free surface. We calculate pr obabilities for the various one-to-one surface scattering processes allowed for a range of energies and compare the scattering rates with those obtain ed when backflow is neglected.