Towards a Nonsingular Bouncing Cosmology

Abstract

We present a nonsingular bouncing cosmology using single scalar field matter with non-trivial potential and non-standard kinetic term. The potential sources a dynamical attractor solution with Ekpyrotic contraction which washes out small amplitude anisotropies. At high energy densities the field evolves into a ghost condensate, leading to a nonsingular bounce. Following the bounce there is a smooth transition to standard expanding radiation and matter dominated phases. Using linear cosmological perturbation theory we track each Fourier mode of the curvature fluctuation throughout the entire cosmic evolution. Using standard matching conditions for nonsingular bouncing cosmologies we verify that the spectral index does not change during the bounce. We show there is a controlled period of exponential growth of the fluctuation amplitude for the perturbations (but not for gravitational waves) around the bounce point which does not invalidate the perturbative treatment. This growth induces a natural suppression mechanism for the tensor to scalar ratio of fluctuations. Moreover, we study the generation of the primordial power spectrum of curvature fluctuations for various types of initial conditions. For the pure vacuum initial condition, on scales which exit the Hubble radius in the phase of Ekpyrotic contraction, the spectrum is deeply blue. For thermal particle initial condition, one possibility for generating a scale-invariant spectrum makes use of a special value of the background equation of state during the contracting Ekpyrotic phase. If the Ekpyrotic phase is preceded by a period of matter-dominated contraction, the primordial power spectrum is nearly scale-invariant on large scales (scales which exit the Hubble radius in the matter-dominated phase) but acquires a large blue tilt on small scales.

21 pages, 11 figures, relevant references added

References in corpus (20)

• Quantum Gravity at a Lifshitz Point
• Imperfect Dark Energy from Kinetic Gravity Braiding
• G-inflation: inflation driven by the Galileon field
• New Ekpyrotic Cosmology
• Galilean Genesis: an alternative to inflation
• Bouncing Universe with Quintom Matter
• Generating Ekpyrotic Curvature Perturbations Before the Big Bang
• Non-singular cosmology in a model of non-relativistic gravity
• A Matter Bounce By Means of Ghost Condensation
• On Perturbations of Quintom Bounce
• Constraints on the Sound Speed of Dynamical Dark Energy
• Evolution of Metric Perturbations in Quintom Bounce model
• A Model Of Inflationary Cosmology Without Singularity
• Thermal Fluctuations and Bouncing Cosmologies
• Unstable growth of curvature perturbation in non-singular bouncing cosmologies
• Cosmological Perturbations on a Bouncing Brane
• On the Transfer of Metric Fluctuations when Extra Dimensions Bounce or Stabilize
• K-Bounce
• On the Transfer of Adiabatic Fluctuations through a Nonsingular Cosmological Bounce
• Perturbations in a regular bouncing Universe

Cited by in corpus (6)

• Dynamical analysis of generalized Galileon cosmology
• The Matter Bounce Alternative to Inflationary Cosmology
• Bounce and cyclic cosmology in extended nonlinear massive gravity
• Emergent Universe Scenario via Quintom Matter
• The Ghost Condensate in N=1 Supergravity
• Lee-Wick radiation induced bouncing universe models