3He impurity excitation spectrum in liquid 4He

We microscopically evaluate the excitation spectrum of the He-3 impurity in liquid He-4 at T=0 and compare it with the experimental curve at equilibrium density. The adopted correlated basis perturbative scheme includes up to two independent phonons, intermediate correlated states, and the correlation operator is built up with two- and three-body correlation functions. The experimental spectrum is well described by the theory along all the available momentum range. A marked deviation from the simple Landau-Pomeranchuck quadratic behavior is found and the momentum-dependent effective mass of the impurity increases by similar to 50% at q similar to 1.7 Angstrom(-1) with respect to its q=0 value. No signature of rotonlike structures is found.