Theoretical study of Bose-Einstein condensates using a new self-consistent perturbation expansion

本文利用一种新的自洽微扰展开方法阐明了单组分玻色-爱因斯坦凝聚体的基本性质。一个被广泛接受的观点是，单粒子激发和双粒子激发是相同的，并由Bogoliubov理论的无隙激发描述。然而，我们发现这两种激发是不同的。本文还发现，由于存在一类新的自能费曼图，李、黄、杨等人关于稀玻色气体基态能量的著名表达式应作修正。

A new self-consistent perturbation expansion, which was developed recently by the principal investigator, has been used to clarify basic properties of a single-component Bose-Einstein condensate. A widely accepted viewpoint on the elementary excitations of the system is that the single- and two-particle excitations are identical and described by the gapless excitation of the Bogoliubov theory. We have found, however, that the two excitations are different from each other. It is also found that the well-known expression on the ground-state energy of a dilute Bose gas by Lee, Huang and Yang should be modified due to a new class of Feynman diagrams for the self-energy.