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Title: Scalar perturbations in the late Universe: viability of the Chaplygin gas models

Abstract

We study the late-time evolution of the Universe where dark energy (DE) is parametrised by a modified generalised Chaplygin gas (mGCG) on top of cold dark matter (CDM) . We also take into account the radiation content of the Universe. In this context, the late stage of the evolution of the universe refers to the epoch where CDM is already clustered into inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies). Under these conditions, the mechanical approach is an adequate tool to study the Universe deep inside the cell of uniformity. To be more accurate, we study scalar perturbations of the Friedmann-Lemaȋtre-Robertson-Walker metric due to inhomogeneities of CDM as well as fluctuations of radiation and mGCG, the later driving the late-time acceleration of the universe. Our analysis applies as well to the case where mGCG plays the role of DM and DE . We select the sets of parameters of the mGCG that are compatible with the mechanical approach. These sets define prospective mGCG models. By comparing the selected sets of models with some of the latest observational data results, we conclude that the mGCG is in tight agreement with those observations particularly for a mGCG playing the rolemore » of DE and DM.« less

Authors:
 [1]; ;  [2];  [3];  [4]
  1. Departamento de Física, Universidade da Beira Interior, 6200 Covilhã (Portugal)
  2. Department of Theoretical Physics, Odessa National University, Dvoryanskaya st. 2, Odessa 65082 (Ukraine)
  3. Department of Theoretical Physics, University of the Basque Country UPV/EHU, P.O. Box 644, 48080 Bilbao (Spain)
  4. Astronomical Observatory, Odessa National University, Dvoryanskaya st. 2, Odessa 65082 (Ukraine)
Publication Date:
OSTI Identifier:
22525119
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2015; Journal Issue: 12; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; COMPARATIVE EVALUATIONS; COSMIC GASES; DISTURBANCES; EVOLUTION; FLUCTUATIONS; GALAXIES; GALAXY CLUSTERS; METRICS; NONLUMINOUS MATTER; SCALARS; UNIVERSE

Citation Formats

Bouhmadi-López, Mariam, Brilenkov, Maxim, Brilenkov, Ruslan, Morais, João, and Zhuk, Alexander, E-mail: mbl@ubi.pt, E-mail: maxim.brilenkov@gmail.com, E-mail: ruslan.brilenkov@gmail.com, E-mail: jviegas001@ikasle.ehu.eus, E-mail: ai.zhuk2@gmail.com. Scalar perturbations in the late Universe: viability of the Chaplygin gas models. United States: N. p., 2015. Web. doi:10.1088/1475-7516/2015/12/037.
Bouhmadi-López, Mariam, Brilenkov, Maxim, Brilenkov, Ruslan, Morais, João, & Zhuk, Alexander, E-mail: mbl@ubi.pt, E-mail: maxim.brilenkov@gmail.com, E-mail: ruslan.brilenkov@gmail.com, E-mail: jviegas001@ikasle.ehu.eus, E-mail: ai.zhuk2@gmail.com. Scalar perturbations in the late Universe: viability of the Chaplygin gas models. United States. doi:10.1088/1475-7516/2015/12/037.
Bouhmadi-López, Mariam, Brilenkov, Maxim, Brilenkov, Ruslan, Morais, João, and Zhuk, Alexander, E-mail: mbl@ubi.pt, E-mail: maxim.brilenkov@gmail.com, E-mail: ruslan.brilenkov@gmail.com, E-mail: jviegas001@ikasle.ehu.eus, E-mail: ai.zhuk2@gmail.com. 2015. "Scalar perturbations in the late Universe: viability of the Chaplygin gas models". United States. doi:10.1088/1475-7516/2015/12/037.
@article{osti_22525119,
title = {Scalar perturbations in the late Universe: viability of the Chaplygin gas models},
author = {Bouhmadi-López, Mariam and Brilenkov, Maxim and Brilenkov, Ruslan and Morais, João and Zhuk, Alexander, E-mail: mbl@ubi.pt, E-mail: maxim.brilenkov@gmail.com, E-mail: ruslan.brilenkov@gmail.com, E-mail: jviegas001@ikasle.ehu.eus, E-mail: ai.zhuk2@gmail.com},
abstractNote = {We study the late-time evolution of the Universe where dark energy (DE) is parametrised by a modified generalised Chaplygin gas (mGCG) on top of cold dark matter (CDM) . We also take into account the radiation content of the Universe. In this context, the late stage of the evolution of the universe refers to the epoch where CDM is already clustered into inhomogeneously distributed discrete structures (galaxies, groups and clusters of galaxies). Under these conditions, the mechanical approach is an adequate tool to study the Universe deep inside the cell of uniformity. To be more accurate, we study scalar perturbations of the Friedmann-Lemaȋtre-Robertson-Walker metric due to inhomogeneities of CDM as well as fluctuations of radiation and mGCG, the later driving the late-time acceleration of the universe. Our analysis applies as well to the case where mGCG plays the role of DM and DE . We select the sets of parameters of the mGCG that are compatible with the mechanical approach. These sets define prospective mGCG models. By comparing the selected sets of models with some of the latest observational data results, we conclude that the mGCG is in tight agreement with those observations particularly for a mGCG playing the role of DE and DM.},
doi = {10.1088/1475-7516/2015/12/037},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 12,
volume = 2015,
place = {United States},
year = 2015,
month =
}
  • We exploit the gauge-invariant formalism to analyse the perturbative behaviour of two cosmological models based on the generalized Chaplygin gas describing both dark matter and dark energy in the present universe. In the first model we consider the generalized Chaplygin gas alone, while in the second one we add a baryon component to it. We extend our analysis also into the parameter range {alpha}>1, where the generalized Chaplygin gas sound velocity can be larger than that of light. In the first model we find that the matter power spectrum is compatible with the observed one only for {alpha}<10{sup -5}, whichmore » makes the generalized Chaplygin gas practically indistinguishable from {Lambda}CDM. In the second model we study the evolution of inhomogeneities of the baryon component. The theoretical power spectrum is in good agreement with the observed one for almost all values of {alpha}. However, the growth of inhomogeneities seems to be particularly favoured either for sufficiently small values of {alpha} or for {alpha}{approx}>3. Thus, it appears that the viability of the generalized Chaplygin gas as a cosmological model is stronger when its sound velocity is superluminal. We show that in this case the generalized Chaplygin gas equation of state can be changed in an unobservable region in such a way that its equivalent k-essence microscopical model has no problems with causality.« less
  • We study the time evolution of small classical perturbations in a gauge-invariant way for a complex scalar field in the early zero-curvature Friedmann-Lema{cflx i}tre universe. We, thus, generalize the analysis which has been done so far for a real scalar field. We give also a derivation of the Jeans wave number in the Newtonian regime starting from the general relativistic equations, avoiding the so-called Jeans swindle. During the inflationary phase, whose length depends on the value of the bosonic charge, the behavior of the perturbations turns out to be the same as for a real scalar field. In the oscillatorymore » phase the time evolution of the perturbations can be determined analytically as long as the bosonic charge of the corresponding background solution is sufficiently large. This is not possible for the real scalar field, since the corresponding bosonic charge vanishes. {copyright} {ital 1997} {ital The American Physical Society}« less
  • Energy-density perturbations in a universe dominated by coherent oscillations of a scalar field evolve as in a pressureless fluid. The analysis applies in particular to axion models. Axions are thus a candidate for cold dark matter.
  • We discuss second-order cosmological perturbations on super-Hubble scales, in a scalar field dominated universe, such as during single field inflation. In this contest we show that the gauge-invariant curvature perturbations defined on uniform density and comoving hypersurfaces coincide and that perturbations are adiabatic in the large scale limit. Since it has been recently shown that the uniform density curvature perturbation is conserved on large scales if perturbations are adiabatic, we conclude that both the uniform density and comoving curvature perturbations at second order, in a scalar field dominated universe, are conserved. Finally, in the light of this result, we commentmore » on the variables recently used in the literature to compute non-Gaussianities.« less
  • We investigate the scalar field perturbations of the 4+1-dimensional Schwarzschild black hole immersed in a Goedel universe, described by the Gimon-Hashimoto solution. This may model the influence of the possible rotation of the universe upon the radiative processes near a black hole. In the regime when the scale parameter j of the Goedel background is small, the oscillation frequency is linearly decreasing with j, while the damping time is increasing. The quasinormal modes are damping, implying stability of the Schwarzschild-Goedel space-time against scalar field perturbations. The approximate analytical formula for large multipole numbers is found.