Density matrix of superfluid 4He and temperature dependence of the static structure factor

The authors computed properties of superfluid 4He on the basis of a new density matrix which is based on a shadow wave function for the roton excitation. They deduce the separate contribution of kinetic and potential energy to a roton and find that a roton lowers the potential energy of the system. They find that S (k;T) and g(r;T) have an anomalous T dependence as found experimentally and the extra correlations present at finite T are induced by rotons. By computing the condensate fraction n0(T), they find that the Cummings et al. relation between g(r;T) and n0(T) is violated and that it leads to a value of n0(T) larger of the true one