Analytic study of cosmological perturbations in a unified model of dark matter and dark energy with a sharp transition

Rodrigo R Cuzinatto,Léo G Medeiros,Eduardo M De Morais,Robert H Brandenberger

doi:10.1016/j.astropartphys.2018.07.005

Rodrigo R Cuzinatto, Léo G Medeiros + Show 2 more

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https://doi.org/10.1016/j.astropartphys.2018.07.005

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Abstract

We study cosmological perturbations in a model of unified dark matter and dark energy with a sharp transition in the late-time universe. The dark sector is described by a dark fluid which evolves from an early stage at redshifts z > zC when it behaves as cold dark matter (CDM) to a late time dark energy (DE) phase (z < zC) when the equation of state parameter is w=−1+ϵ, with a constant ϵ which must be in the range 0 < ϵ < 2/3. We show that fluctuations in the dark energy phase suffer from an exponential instability, the mode functions growing both as a function of comoving momentum k and of conformal time η. In order that this exponential instability does not lead to distortions of the energy density power spectrum on scales for which we have good observational results, the redshift zC of transition between the two phases is constrained to be so close to zero that the model is unable to explain the supernova data.

Highlights

Observations of large scale structure [1, 2] are consistent with a cosmological model where cold dark matter (CDM) dominates the evolution of the universe after recombination
Magnitude-redshift studies of supernovae of type Ia (SNIa) [3, 4] indicate that the universe’s expansion is currently accelerating. This demands the presence of an exotic component dubbed dark energy (DE) which has an equation of state close to that of a cosmological constant and which dominates the energy density at the present time
The purpose of this paper is to study the constraints for our quartessence models which come from demanding consistency with the observed density power power spectrum

Summary

Introduction

Observations of large scale structure [1, 2] are consistent with a cosmological model where cold dark matter (CDM) dominates the evolution of the universe after recombination. Magnitude-redshift studies of supernovae of type Ia (SNIa) [3, 4] indicate that the universe’s expansion is currently accelerating. This demands the presence of an exotic component dubbed dark energy (DE) which has an equation of state close to that of a cosmological constant and which dominates the energy density at the present time. This component affects the detailed peak structure of the angular power spectrum of cosmic microwave background radiation (CMB) anisotropies The current data (see e.g. [9]) give detailed support of the current picture in which the universe is dominated by CDM until the DE component takes over in the recent past

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Discussion

Conclusion