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arXiv · 2311.08073

$\delta N$ formalism on the past light-cone

Giuseppe Fanizza·Giovanni Marozzi·Matheus Medeiros
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Abstract

We apply the gradient expansion approximation to the light-cone gauge, obtaining a separate universe picture at non-linear order in perturbation theory within this framework. Thereafter, we use it to generalize the $\delta N$ formalism in terms of light-cone perturbations. As a consistency check, we demonstrate the conservation of the gauge invariant curvature perturbation on uniform density hypersurface $\zeta$ at the completely non-linear level. The approach studied provides a self-consistent framework to connect at non-linear level quantities from the primordial universe, such as $\zeta$, written in terms of the light-cone parameters, to late time observables.

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Giuseppe Fanizza, Giovanni Marozzi, Matheus Medeiros. 2023-11-14. $\delta N$ formalism on the past light-cone. https://doi.org/10.1007/s10714-024-03239-3

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