Effective Mass of Atom and Excitation Spectrum in Liquid Helium-4 at T=0   K
  A self-consistent approach is applied for the calculations within the two-time temperature Green functions formalism in the random phase approximation. The effective mass of He4 atom is computed as $m^*=1.58 m$. The excitation spectrum is found to be in a satisfactory agreement with the experiment. The sound velocity is calculated as 230 m/s. The temperature of the Bose-condensation with the effective mass taken into consideration is estimated as 1.99 K. 
A. A. Rovenchak