887 research outputs found
Quantum cosmology and late-time singularities
The development of dark energy models has stimulated interest to cosmological
singularities, which differ from the traditional Big Bang and Big Crunch
singularities. We review a broad class of phenomena connected with soft
cosmological singularities in classical and quantum cosmology. We discuss the
classification of singularities from the geometrical point of view and from the
point of view of the behaviour of finite size objects, crossing such
singularities. We discuss in some detail quantum and classical cosmology of
models based on perfect fluids (anti-Chaplygin gas and anti-Chaplygin gas plus
dust), of models based on the Born-Infeld-type fields and of the model of a
scalar field with a potential inversely proportional to the field itself. We
dwell also on the phenomenon of the phantom divide line crossing in the scalar
field models with cusped potentials. Then we discuss the Friedmann equations
modified by quantum corrections to the effective action of the models under
considerations and the influence of such modification on the nature and the
existence of soft singularities. We review also quantum cosmology of models,
where the initial quantum state of the universe is presented by the density
matrix (mixed state). Finally, we discuss the exotic singularities arising in
the brane-world cosmological models.Comment: final version, published in Classical and Quantum Gravity as a
topical revie
The problem of singularities and chaos in cosmology
We consider different aspects of the problem of cosmological singularity such
as the BKL oscillatory approach to the singularity, the new features of the
cosmological dynamics in the neighbourhood of the singularity in
multidimensional and superstring cosmological models and their connections with
such a modern branch of mathematics as infinite-dimensional Lie algebras. The
chaoticity of the oscillatory approach to the cosmological singularity is also
discussed. The Conclusion contains some thoughts about the past and the future
of the Universe in the light of the oscillatory approach to the Big Bang and
the Big Crunch cosmological singularities.Comment: 17 page
Relativistic hodograph equation for a two-dimensional stationary isentropic hydrodynamical motion
We derive a relativistic hodograph equation for a two-dimensional stationary
isentropic hydrodynamical motion. For the case of stiff matter, when the
velocity of sound coincides with the light speed, the singularity in this
equation disappears and the solutions become regular in all hodograph plane.Comment: 5 page
Chameleon Cosmology Model Describing the Phantom Divide Line Crossing
An exact solution describing the evolution of the type Bang-to-Rip with the
phantom divide line crossing is constructed in the Chameleon cosmology model,
based on two independent functions of the scalar field.Comment: 9 page
Exact solutions of the Einstein equations for an infinite slab with a constant energy density
We find exact static solutions of the Einstein equations in the spacetime
with plane symmetry, where an infinite slab with finite thickness and
homogeneous energy (mass) density is present. In the first solution the
pressure is isotropic, while in the second solution the tangential components
of the pressure are equal to zero. In both cases the pressure vanishes at the
boundaries of the slab. Outside the slab these solutions are matched with the
Rindler spacetime and with the Weyl-Levi-Civita spacetime, which represent
special cases of the Kasner solution.Comment: Final version, published in Physics Letters
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