Gravitational Stability and Bulk Cosmology
| dc.creator | Carlevaro, Nakia | |
| dc.creator | Montani, Giovanni | |
| dc.date | 2007-10-01 | |
| dc.date | 2007-12-05 | |
| dc.date.accessioned | 2026-07-07T12:54:57Z | |
| dc.date.available | 2026-07-07T12:54:57Z | |
| dc.description | We present a discussion of the effects induced by bulk viscosity either on the very early Universe stability and on the dynamics associated to the extreme gravitational collapse of a gas cloud. In both cases the viscosity coefficient is related to the energy density $ρ$ via a power-law of the form $ζ=ζ_0 ρ^s$ (where $ζ_0, s=const.$) and the behavior of the density contrast in analyzed. In the first case, matter filling the isotropic and homogeneous background is described by an ultra-relativistic equation of state. The analytic expression of the density contrast shows that its growth is suppressed forward in time as soon as $ζ_0$ overcomes a critical value. On the other hand, in such a regime, the asymptotic approach to the initial singularity admits an unstable collapsing picture. In the second case, we investigate the top-down fragmentation process of an uniform and spherically symmetric gas cloud within the framework of a Newtonian approach, including the negative pressure contribution associated to the bulk viscous phenomenology. In the extreme regime toward the singularity, we show that the density contrast associated to an adiabatic-like behavior of the gas (which is identified by a particular range of the politropic index) acquire, for sufficiently large viscous contributions, a vanishing behavior which prevents the formation of sub-structures. Such a feature is not present in the isothermal-like collapse. We also emphasize that in the adiabatic-like case bulk viscosity is also responsible for the appearance of a threshold scale (equivalent to a Jeans length) beyond which perturbations begin to increase. | |
| dc.description | 13 pages, no figure | |
| dc.identifier | https://arxiv.org/abs/0710.0313 | |
| dc.identifier | http://arxiv.org/abs/0710.0313 | |
| dc.identifier | AIP Conf. Proc. 966, 241-248 (2008) | |
| dc.identifier | doi:10.1063/1.2837002 | |
| dc.identifier.uri | http://salesiana.dossiersoluciones.com/handle/123456789/224116 | |
| dc.subject | General Relativity and Quantum Cosmology | |
| dc.subject | Astrophysics | |
| dc.title | Gravitational Stability and Bulk Cosmology | |
| dc.type | text |