### Abstract

We develop a theory of nonlinear cosmological perturbations on superhorizon scales for a multicomponent scalar field with a general kinetic term and a general form of the potential in the context of inflationary cosmology. We employ the ADM formalism and the spatial gradient expansion approach, characterized by O(ε^{2}), where ε = 1/(HL) is a small parameter representing the ratio of the Hubble radius to the characteristic length scale L of perturbations. We provide a formalism to obtain the solution in the multi-field case. This formalism can be applied to the superhorizon evolution of a primordial non-Gaussianity beyond the so-called δN formalism which is equivalent to O(ε ^{0}) of the gradient expansion. In doing so, we also derive fully nonlinear gauge transformation rules valid through O(ε ^{2}). These fully nonlinear gauge transformation rules can be used to derive the solution in a desired gauge from the one in a gauge where computations are much simpler. As a demonstration, we consider an analytically solvable model and construct the solution explicitly.

Original language | English |
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Article number | 043E01 |

Journal | Progress of Theoretical and Experimental Physics |

Volume | 2013 |

Issue number | 4 |

DOIs | |

Publication status | Published - 2013 Apr 1 |

### ASJC Scopus subject areas

- Physics and Astronomy(all)

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## Cite this

*Progress of Theoretical and Experimental Physics*,

*2013*(4), [043E01]. https://doi.org/10.1093/ptep/ptt008