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Abstract: In this paper we study the evolution of cosmological perturbations in thepresence of dynamical dark energy, and revisit the issue of dark energyperturbations. For a generally parameterized equation of state EoS such asw Dz = w 0+w 1\frac{z}{1+z}, for a single fluid or a single scalar field the dark energy perturbation diverges when its EoS crosses the cosmologicalconstant boundary w D=-1. In this paper we present a method of treating thedark energy perturbations during the crossing of the $w D=-1$ surface byimposing matching conditions which require the induced 3-metric on thehypersurface of w D=-1 and its extrinsic curvature to be continuous. Thesematching conditions have been used widely in the literature to studyperturbations in various models of early universe physics, such as Inflation,the Pre-Big-Bang and Ekpyrotic scenarios, and bouncing cosmologies. In all ofthese cases the EoS undergoes a sudden change. Through a detailed analysis ofthe matching conditions, we show that \delta D and \theta D are continuous onthe matching hypersurface. This justifies the method used1-4 in the numericalcalculation and data fitting for the determination of cosmological parameters.We discuss the conditions under which our analysis is applicable.

Autor: Mingzhe Li, Yifu Cai, Hong Li, Robert Brandenberger, Xinmin Zhang

Fuente: https://arxiv.org/

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