Helium-4 Energy and Specific Heat in Superfluid and Normal Phase
  The calculation of the He4 energy and specific heat is carried out in a wide temperature range within the two-time temperature Green functions approach. The approximation improving the random phase approximation is developed providing the correct behaviour of the calculated specific heat at the temperatures $0 < T/T_c < 0.65$ and $T/T_c> 1.32$ where $T_c$ stands for the phase transition point. 
A. A. Rovenchak