Cosmological Perturbations Through a Non-Singular Ghost-Condensate/Galileon Bounce

Abstract

We study the propagation of super-horizon cosmological perturbations in a non-singular bounce spacetime. The model we consider combines a ghost condensate with a Galileon term in order to induce a ghost-free bounce. Our calculation is performed in harmonic gauge, which ensures that the linearized equations of motion remain well-defined and non-singular throughout. We find that, despite the fact that near the bounce the speed of sound becomes imaginary, super-horizon curvature perturbations remain essentially constant across the bounce. In fact, we show that there is a time close to the bounce where curvature perturbations of all wavelengths are required to be momentarily exactly constant. We relate our calculations to those performed in other gauges, and comment on the relation to previous results in the literature.

28 pages, 16 figures, v2: references added

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• Matter bounce cosmology with a generalized single field: non-Gaussianity and an extended no-go theorem
• Cuscuton gravity as a classically stable limiting curvature theory
• Non-singular Bounce Cosmology from Lagrange Multiplier $F(R)$ Gravity
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• Classical Inflationary and Ekpyrotic Universes in the No-Boundary Wavefunction
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• Non-Singular Bounces Catalysed by Dark Energy
• Quantum Circuit Complexity of Primordial Perturbations
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• Towards a Solution of the Negative Mode Problem in Quantum Tunnelling with Gravity
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• Massive gravity and the suppression of anisotropies and gravitational waves in a matter-dominated contracting universe
• Perturbations in generalized Galileon theories
• Creation of wormholes by quantum tunnelling in modified gravity theories
• A gauge invariant prescription to avoid $\gamma$-crossing instability in Galileon bounce