Comment on perturbations during a regular bounce
Abstract
We point out an inconsistency of a method used in the literature, first advocated by P. Peter and N. PintoNeto in [Phys. Rev. D 66, 063509 (2002)], for studying adiabatic scalar perturbations in a regular bouncing universe (in four dimensions). The method under scrutiny consists of splitting the Bardeen potential into two pieces with independent evolutions, in order to avoid a singular behavior at the boundaries of the region where the null energy condition (NEC) is violated. However, we argue that this method violates energymomentum conservation. We then introduce a novel method which provides two independent solutions for the Bardeen potential around the boundaries, even in the case of adiabatic perturbations. The two solutions are well behaved and not divergent.
 Authors:
 Physics Department, Brown University, Providence, Rhode Island 02912 (United States)
 Department of Physics, University of Wisconsin, Madison, Wisconsin 53706 (United States)
 Publication Date:
 OSTI Identifier:
 20776814
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Physical Review. D, Particles Fields; Journal Volume: 73; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevD.73.048501; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; COSMOLOGY; DISTURBANCES; EVOLUTION; MATHEMATICAL SOLUTIONS; POTENTIALS; SCALARS; UNIVERSE
Citation Formats
Battefeld, Thorsten J., and Geshnizjani, Ghazal. Comment on perturbations during a regular bounce. United States: N. p., 2006.
Web. doi:10.1103/PhysRevD.73.048501.
Battefeld, Thorsten J., & Geshnizjani, Ghazal. Comment on perturbations during a regular bounce. United States. doi:10.1103/PhysRevD.73.048501.
Battefeld, Thorsten J., and Geshnizjani, Ghazal. Wed .
"Comment on perturbations during a regular bounce". United States.
doi:10.1103/PhysRevD.73.048501.
@article{osti_20776814,
title = {Comment on perturbations during a regular bounce},
author = {Battefeld, Thorsten J. and Geshnizjani, Ghazal},
abstractNote = {We point out an inconsistency of a method used in the literature, first advocated by P. Peter and N. PintoNeto in [Phys. Rev. D 66, 063509 (2002)], for studying adiabatic scalar perturbations in a regular bouncing universe (in four dimensions). The method under scrutiny consists of splitting the Bardeen potential into two pieces with independent evolutions, in order to avoid a singular behavior at the boundaries of the region where the null energy condition (NEC) is violated. However, we argue that this method violates energymomentum conservation. We then introduce a novel method which provides two independent solutions for the Bardeen potential around the boundaries, even in the case of adiabatic perturbations. The two solutions are well behaved and not divergent.},
doi = {10.1103/PhysRevD.73.048501},
journal = {Physical Review. D, Particles Fields},
number = 4,
volume = 73,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2006},
month = {Wed Feb 15 00:00:00 EST 2006}
}

We present a study of a simple scalar field model that yields nonsingular cosmological solutions. We study both the qualitative dynamics of the homogeneous and isotropic background and the evolution of inhomogeneous linear perturbations. We calculate the spectrum of perturbations generated on superHubble scales during the collapse phase from initial vacuum fluctuations on small scales and then evolve these numerically through the bounce. We show that the comoving curvature perturbation calculated during the collapse phase provides a good estimate of the resulting large scale adiabatic perturbation in the expanding phase while the Bardeen metric potential is dominated by what becomesmore »

Evolution of linear perturbations through a bouncing world model: Is the near HarrisonZel'dovich spectrum possible via a bounce?
We present a detailed numerical study of the evolutions of cosmological linear perturbations through a simple bouncing world model based on two scalar fields. We properly identify the relatively growing and decaying solutions in expanding and collapsing phases. Using a decomposition based on the largescale limit exact solution of curvature (adiabatic) perturbations with two independent modes, we assign the relatively growing/decaying one in an expanding phase as the C/dmode. In the collapsing phase, the roles are reversed, and the C/dmode is relatively decaying/growing. The analytic solution shows that, as long as the largescale and the adiabatic conditions are met, themore » 
On perturbations of a quintom bounce
A quintom universe with an equation of state crossing the cosmological constant boundary can provide a bouncing solution dubbed the quintom bounce and thus resolve the big bang singularity. In this paper, we investigate the cosmological perturbations of the quintom bounce both analytically and numerically. We find that the fluctuations in the dominant mode in the postbounce expanding phase couple to the growing mode of the perturbations in the prebounce contracting phase. 
Perturbations in matter bounce with nonminimal coupling
In this paper, we investigate the perturbations in matter bounce induced from LeeWick lagrangian with the involvement of nonminimal coupling to the Einstein Gravity. We find that this extra nonminimal coupling term can cause a redtilt on the primordial metric perturbation at extremely large scales. It can also lead to large enhancement of reheating of the normal field particles compared to the usual minimal coupling models. 
Cosmological perturbations through a nonsingular ghostcondensate/Galileon bounce
We study the propagation of superhorizon cosmological perturbations in a nonsingular bounce spacetime. The model we consider combines a ghost condensate with a Galileon term in order to induce a ghostfree bounce. Our calculation is performed in harmonic gauge, which ensures that the linearized equations of motion remain welldefined and nonsingular throughout. We find that, despite the fact that near the bounce the speed of sound becomes imaginary, superhorizon 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 bemore »