Brandow Boson Linked-Cluster Expansion Applied to the High-Density Charged Boson Gas

The Brandow boson linked-cluster expansion has been used to redo the Foldy calculation of the Bogoliubov theory for a charged boson gas. The particle-number conservation is treated exactly. The ring diagrams have been summed using the same techniques as used by Gell-Mann and Brueckner for the electron gas. The next-most-divergent diagrams (twisted rings) have also been summed. These diagrams contain a renormalized hole line and thus show explicitly the dynamics of the condensate which is treated only in an average way in the Bogoliubov theory. The results for the ground-state energy and the condensation fraction agree exactly with Foldy in the high-density limit.