Bianchi type I 宇宙模型探討

Robert Wald showed that anisotropically expanding universes will evolve to a stable de Sitter space for a large class of Einstein gravity models with a positive cosmological constant under certain energy conditions. A detailed review is presented in this paper. It is also found that a class of Bianchi type I expanding solutions exist in the presence of the higher derivative corrections. We provide a detailed derivation of the field equations, and solve for the expanding solutions in a systematic manner. This class of anisotropically expanding soltuions are shown to be unstable by perturbating the field equations in the presence of the expanding background solution.