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A self-consistent approach is applied for the calculations within thetwo-time temperature Green functions formalism in the random phaseapproximation. The effective mass of He4 atom is computed as $m^*=1.58 m$. Theexcitation spectrum is found to be in a satisfactory agreement with theexperiment. The sound velocity is calculated as 230 m/s. The temperature of theBose-condensation with the effective mass taken into consideration is estimatedas 1.99 K.Comment: 5 pages, 1 figur

Effective mass of atom and the excitation spectrum in liquid helium-4 at T=0 K