POLARSKI David
Fonction : Permanent
Organisme : Université Montpellier II
Professeur
(HDR)
David.POLARSKI
umontpellier.fr
0467149329
Bureau: 10, Etg: 1, Bât: 13  Site : Campus Triolet
Domaines de Recherche:  Physique/Relativité Générale et Cosmologie Quantique

Dernieres productions scientifiques :


Bouncing Universes in ScalarTensor Gravity Around Conformal Invariance
Auteur(s): Bruno Boisseau, Giacomini Hector, Polarski D.
(Document sans référence bibliographique) 20160323
Ref HAL: hal01292660_v1
Ref Arxiv: 1603.06648v1
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: We consider the possibility to produce a bouncing universe in the framework of scalartensor gravity when the scalar field has a nonconformal coupling to the Ricci scalar. We prove that bouncing universes regular in the future with essentially the same dynamics as for the conformal coupling case do exist when the coupling deviates slightly from it. This is found numerically for more substantial deviations as well. In some cases however new features are found like the ability of the system to leave the effective phantom regime.



Scalar field cosmologies with inverted potentials
Auteur(s): Boisseau Bruno, Giacomini Hector, Polarski D.
(Article) Publié:
Journal Of Cosmology And Astroparticle Physics, vol. p. (2015)
Ref HAL: hal01266923_v1
DOI: 10.1088/14757516/2015/10/033
Exporter : BibTex  endNote
3 citations
Résumé: Regular bouncing solutions in the framework of a scalartensor gravity model were found in a recent work. We reconsider the problem in the Einstein frame (EF) in the present work. Singularities arising at the limit of physical viability of the model in the Jordan frame (JF) are either of the Big Bang or of the Big Crunch type in the EF. As a result we obtain integrable scalar field cosmological models in general relativity (GR) with inverted doublewell potentials unbounded from below which possess solutions regular in the future, tending to a de Sitter space, and starting with a Big Bang. The existence of the two fixed points for the field dynamics at late times found earlier in the JF becomes transparent in the EF.



Bouncing universes in scalartensor gravity models admitting negative potentials
Auteur(s): Boisseau B., Giacomini H., Polarski D., Starobinsky A. A.
(Article) Publié:
Journal Of Cosmology And Astroparticle Physics, vol. 2015 p.002 (2015)
Ref HAL: hal01203042_v1
DOI: 10.1088/14757516/2015/07/002
Exporter : BibTex  endNote
12 citations
Résumé: We consider the possibility to produce a bouncing universe in the framework of scalartensor gravity models in which the scalar field potential may be negative, and even unbounded from below. We find a set of viable solutions with nonzero measure in the space of initial conditions passing a bounce, even in the presence of a radiation component, and approaching a constant gravitational coupling afterwards. Hence we have a model with a minimal modification of gravity in order to produce a bounce in the early universe with gravity tending dynamically to general relativity (GR) after the bounce.



The complementarity of the redshift drift
Auteur(s): Moraes Bruno, Polarski D.
(Document sans référence bibliographique) 20111011
Ref HAL: hal00632611_v1
Ref Arxiv: 1110.2525
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: We derive some basic equations related to the redshift drift and we show how some dark energy (DE) properties can be retrieved from it. We consider in particular three kinds of DE models which exhibit a characteristic signature in their redshift drift while no such signature would be present in their luminositydistances: a sudden change of the equation of state parameter w_{DE} at low redshifts, oscillating DE and finally an equation of state with spikes at low redshifts. Accurate redshift drift measurements would provide interesting complementary probes for some of these models and for models with varying gravitational coupling. While the redshift drift would efficiently constrain models with a spike at z~1, the signature of the redshift drift for models with large variations at very low redshifts z<0.1 would be unobservable, allowing a large arbitrariness in the present expansion of the universe.
Commentaires: Accepted for publication in Phys. Rev. D; 12 pages, 8 figures



Dark Energy
Auteur(s): Polarski D.
Conférence invité: Quantum gravity (Ioannina, GR, 20100607)
Actes de conférence: Journall of Physics: Conference Series, vol. 283 p.012029 ()
Ref HAL: hal00632711_v1
Exporter : BibTex  endNote
Résumé: A large number of observations suggest that our universe entered at low redshifts a stage with accelerated expansion rate. Many models, Dark Energy (DE) models, able to explain this departure from conventional cosmology have been proposed. These models are conceptually very different, either introducing some new component with sufficiently negative pressure, or modifying the gravitational interaction on cosmic scales. Some of these DE models are reviewed here. Future high precision observations probing both the background and the perturbations will single out viable models.

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