MG15 - Talk detail |
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Participant |
Kamenshchik, Alexander | |||||||
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Institution |
University of Bologna, Department of Physics and Astronomy - via Irnerio 46 - Bologna - - Italy | |||||||
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Session |
DE1 |
Accepted |
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Talk |
Oral abstract |
Title |
Singularity crossing, transformation of matter properties and the problem of parametrization in field theories | |||||
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Abstract |
We investigate particular cosmological models, based either on tachyon fields or on perfect fluids, for which soft future singularities arise in a natural way. Our main result is the description of a smooth crossing of the soft singularity in models with an anti-Chaplygin gas or with a particular tachyon field in the presence of dust. Such a crossing is made possible by certain transformations of matter properties. We discuss and compare also different approaches to the problem of crossing of the Big Bang - Big Crunch singularities. |
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Session |
AT1 |
Accepted |
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Oral abstract |
Title |
Darkness without dark matter and energy -- generalized unimodular gravity | |||||
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Abstract |
We suggest a Lorentz non-invariant generalization of the unimodular gravity theory, which is classically equivalent to general relativity with a locally inert (devoid of local degrees of freedom) perfect fluid having an equation of state with a constant parameter w. For the range of w near −1 this dark fluid can play the role of dark energy, while for w=0 this dark dust admits spatial inhomogeneities and can be interpreted as dark matter. |
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Session |
EU2 |
Accepted |
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Oral abstract |
Title |
Quantum Gravity, Time, Bounces and Matter | |||||
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Abstract |
In the context of Quantum Cosmology and the Wheeler-DeWitt equation we investigate the possible effects of a non semiclassical wave-function of the universe on the evolution of the inflationary perturbations. These are associated with the quantum behaviour of the homogenous degrees of freedom (in particular the radius of the universe) in the early stages of the inflationary expansion, which in turn can affect the dynamics of the trans-Planckian modes of the fields present. The existence of a bounce for the homogeneous gravitational wave-function is studied. This can lead to an interference between a contracting and an expanding universe and, as a consequence, to the above quantum gravitational effects on the primordial spectra. In the traditional study of the inflationary fluctuations such effects are neglected and a quasi-classical behaviour for the homogeneous inflaton-gravity system is taken. |
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