A Quantum Field Theory approach to simple liquids: The elementary excitations of helium 4

In the framework of Quantum Field Theory we propose a novel approach to the theory of bosonic simple liquids, formulated in terms of a scalar, complex quantum field, the wvave-field Psi (x, t). The problem is treated in a mean-held approximation, diagonalizing the quadratic part of the Hamiltonian a la Bogoliubov and calculating in a perturbative scheme the one-loop correction to the self-energy function. We derive the dispersion relation and the dynamic and static structure factors of the liquid He-4, obtaining results that are successfully compared with experimental data.