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arXiv · 1612.00346

Stringy bounces and gradient instabilities

Massimo Giovannini
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Abstract

Bouncing solutions are obtained from a generally covariant action characterized by a potential which is a nonlocal functional of the dilaton field at two separated space-time points. Gradient instabilities are shown to arise in this context but they are argued to be nongeneric. After performing a gauge-invariant and frame-invariant derivation of the evolution equations of the fluctuations, a heuristic criterion for the avoidance of pathological instabilities is proposed and corroborated by a number of explicit examples that turn out to be compatible with a quasi-flat spectrum of curvature inhomogeneities for typical wavelengths larger than the Hubble radius.

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Massimo Giovannini. 2016-12-01. Stringy bounces and gradient instabilities. https://doi.org/10.1103/physrevd.95.083506

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