Consistent perturbations in an imperfect fluid

• Verfasst von: Sawicki, Ignacy [VerfasserIn]
• Verfasst von: Amendola, Luca [VerfasserIn]
• Titel: Consistent perturbations in an imperfect fluid
• Verf.angabe: Ignacy Sawicki, Ippocratis D. Saltas, Luca Amendola and Martin Kunz
• E-Jahr: 2013
• Jahr: 2 January 2013
• Umfang: 55 S.
• Fussnoten: Gesehen am 13.11.2017
• Titel Quelle: Enthalten in: Journal of cosmology and astroparticle physics
• Ort Quelle: London : IOP, 2003
• Jahr Quelle: 2013
• Band/Heft Quelle: (2013), 1, Artikel-ID 004, Seite 1-55
• ISSN Quelle: 1475-7516
• DOI: doi:10.1088/1475-7516/2013/01/004
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1565256840

Abstract

We present a new prescription for analysing cosmological perturbations in a more-general class of scalar-field dark-energy models where the energy-momentum tensor has an imperfect-fluid form. This class includes Brans-Dicke models, f ( R ) gravity, theories with kinetic gravity braiding and generalised galileons. We employ the intuitive language of fluids, allowing us to explicitly maintain a dependence on physical and potentially measurable properties. We demonstrate that hydrodynamics is not always a valid description for describing cosmological perturbations in general scalar-field theories and present a consistent alternative that nonetheless utilises the fluid language. We apply this approach explicitly to a worked example: k- essence non-minimally coupled to gravity. This is the simplest case which captures the essential new features of these imperfect-fluid models. We demonstrate the generic existence of a new scale separating regimes where the fluid is perfect and imperfect. We obtain the equations for the evolution of dark-energy density perturbations in both these regimes. The model also features two other known scales: the Compton scale related to the breaking of shift symmetry and the Jeans scale which we show is determined by the speed of propagation of small scalar-field perturbations, i.e. causality, as opposed to the frequently used definition of the ratio of the pressure and energy-density perturbations.