2016/09/30 by Alireza Talebian-Ashkezari, A. Talebian-Ashkezari, Nahid Ahmadi +3 · 16 citations
Physics and Astronomy · #Anisotropy #Astronomy and Astrophysical Research #Cosmological perturbation theory #Cosmology #Cosmology and Gravitation Theories #Curvature #Equations of motion #Formalism (music) #Galaxies: Formation, Evolution, Phenomena #Inflation (cosmology) #Perturbation (astronomy) #Tensor (intrinsic definition) #astro-ph.CO #gr-qc
paper · pdf · doi:10.1088/1475-7516/2018/03/001
published in Journal of Cosmology and Astroparticle Physics 2018(03), 001 (Institute of Physics) · 35 pages, 2 figures
openalex publication_date 2018/03/05 · arxiv created 2018/03/10 · arxiv updated 2018/03/13 · openalex created_date 2018/03/29 · openalex updated_date 2026/08/05
We study the evolution of the metric perturbations in a Bianchi background in the long-wavelength limit. By applying the gradient expansion to the equations of motion we exhibit a generalized “Separate Universe” approach to the cosmological perturbation theory. Having found this consistent separate universe picture, we introduce the δ M formalism for calculating the evolution of the linear tensor perturbations in anisotropic inflation models in almost the same way that the so-called δ N formula is applied to the super-horizon dynamics of the curvature perturbations. Similar to her twin formula, δ N , this new method can substantially reduce the amount of calculations related to the evolution of tensor modes. However, it is not as general as δ N ; it is a “perturbative" formula and solves the shear only to linear order. In other words, it is restricted to weak shear limit.