Fluctuations of Bose-condensate in nonideal gas

The canonical distribution with constraint is applied to the Bogolubov model of a nonideal Bose-gas. Two solutions of variational equations for Bose-condensate density and constraint parameter are found and treated as the “nontrivial” and “trivial” parts of the process of Bose-condensation. The corresponding branches of the spectrum are investigated. The heat capacity CV is considered with the help of the derived solutions for all the temperatures. The asymptotics of CV for the temperature close to zero and close to critical temperature Tc below and above it are calculated.