Bulk viscous matter-dominated Universes: asymptotic properties
16
Citation
53
Reference
10
Related Paper
Citation Trend
Abstract:
By means of a combined use of the type Ia supernovae and H(z) data tests, together with the study of the asymptotic properties in the equivalent phase space — through the use of the dynamical systems tools — we demonstrate that the bulk viscous matter-dominated scenario is not a good model to explain the accepted cosmological paradigm, at least, under the parametrization of bulk viscosity considered in this paper. The main objection against such scenarios is the absence of conventional radiation and matter-dominated critical points in the phase space of the model. This entails that radiation and matter dominance are not generic solutions of the cosmological equations, so that these stages can be implemented only by means of unique and very specific initial conditions, i. e., of very unstable particular solutions. Such a behavior is in marked contradiction with the accepted cosmological paradigm which requires of an earlier stage dominated by relativistic species, followed by a period of conventional non-relativistic matter domination, during which the cosmic structure we see was formed. Also, we found that the bulk viscosity is positive just until very late times in the cosmic evolution, around z < 1. For earlier epochs it is negative, been in tension with the local second law of thermodynamics.Keywords:
Volume viscosity
Parametrization (atmospheric modeling)
Volume viscosity
Cite
Citations (2)
Chaplygin gas
Friedmann–Lemaître–Robertson–Walker metric
Volume viscosity
Friedmann equations
Cite
Citations (91)
Volume viscosity
Isentropic process
Cite
Citations (83)
Chaplygin gas
Friedmann–Lemaître–Robertson–Walker metric
Volume viscosity
Friedmann equations
Viscous liquid
Cite
Citations (93)
Volume viscosity
Cite
Citations (69)
Volume viscosity
Cite
Citations (3)
Abstract We study varying forms of viscous dark matter (DM) and try to address the intriguing tensions of the standard model of cosmology with recent cosmological data, including the Hubble and S 8 tensions. We note that by assuming the DM viscosity depends on the Hubble parameter, DM density, or both, one can improve the statistics. Although the models tend to aggravate the Hubble tension a bit, they tend to reduce the S 8 tension, even in comparison with the constant viscosity case. Since similar-to-viscosity massive neutrinos suppress the power spectrum of matter on small length scales, considering them along with the viscous DM, we find that the neutrino mass range is tightened.
Volume viscosity
Cold dark matter
Tension (geology)
Cite
Citations (3)
Abstract A simplified parametrization of effective sizes of cirrus‐cloud particles is developed in terms of the ice‐water content and the cloud temperature based on some earlier studies. the effective particle sizes of the cirrus clouds determined using the simplified parametrization are compared with the results determined from observations. the results are generally encouraging. The simplified parametrization is further tested by incorporating it into a new ice‐cloud optical‐property parametrization scheme and performing radiative‐transfer calculations. the results show that this scheme in conjunction with the ice‐cloud optical‐properties scheme can generate a reasonably good estimate of cirrus‐cloud radiative properties compared with the observations.
Parametrization (atmospheric modeling)
Cirrus
Cloud physics
Optical depth
Ice cloud
Cite
Citations (68)
Dark energy of phantom or quintessence nature with an equation of state parameter $w$ almost equal to $\ensuremath{-}1$ often leads the universe evolution to a finite-time future singularity. An elegant solution to this problem has been recently proposed [P. H. Frampton, K. J. Ludwick, and R. J. Scherrer, Phys. Rev. D 84, 063003 (2011).] under the form of the so-called little rip cosmology, which appears to be a realistic alternative to the $\ensuremath{\Lambda}\mathrm{CDM}$ model. A viscous little rip cosmology is here proposed. Whereas generically bulk viscosity tends to promote the big rip, we find that there are a number of situations where this is not the case and where the formalism nicely adjusts itself to the little rip scenario. We prove, in particular, that a viscous fluid (or, equivalently, one with an inhomogeneous [imperfect] equation of state) is perfectly able to produce a little rip cosmology as a purely viscosity effect. The possibility of its induction as a combined result of viscosity and a general (powerlike) equation of state is also investigated in detail. To finish, a physical, inertial force interpretation of the dissolution of bound structures in the little rip cosmology is presented.
Quintessence
Volume viscosity
Cite
Citations (227)