Accurate description of excitations in superfluid He-4

An accurate quantitative description of the maxon-roton excitations in superfluid He-4 is still an open many-body problem. We present a new variational Monte Carlo calculation of this extraction spectrum. Our calculation starts from a shadow wave function in which all the pseudopotentials are optimized with a basis set method. The phase factors of the excitation are induced in the subsidiary variables and an explicit backflow term is also introduced. The computed excitation spectrum is in good agreement with experiment at all wave vectors, the deviations being at the level of 5%. Double roton excitations and strength of the single excitation peak are also computed.