delta M formalism: a new approach to cosmological perturbation theory in anisotropic inflation

作者：Talebian Ashkezari A^*; Ahmadi N; Abolhasani A A

来源：Journal of Cosmology and Astroparticle Physics, 2018, 2018(3): 001.

DOI：10.1088/1475-7516/2018/03/001

• cosmological perturbation theory
• inflation

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 delta N formalism for calculating the evolution of the linear tensor perturbations in anisotropic inflation models in almost the same way that the so-called delta N formula is applied to the super-horizon dynamics of the curvature perturbations. Similar to her twin formula, delta 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 delta N; it is a "perturbative" formula and solves the shear only to linear order. In other words, it is restricted to weak shear limit.

• 出版日期2018-3