Fluid observers and tilting cosmology

Abstract

We study perfect fluid cosmological models with a constant equation of state parameter $\gamma$ in which there are two naturally defined time-like congruences, a geometrically defined geodesic congruence and a non-geodesic fluid congruence. We establish an appropriate set of boost formulae relating the physical variables, and consequently the observed quantities, in the two frames. We study expanding spatially homogeneous tilted perfect fluid models, with an emphasis on future evolution with extreme tilt. We show that for ultra-radiative equations of state (i.e., $\gamma >4/3$), generically the tilt becomes extreme at late times and the fluid observers will reach infinite expansion within a finite proper time and experience a singularity similar to that of the big rip. In addition, we show that for sub-radiative equations of state (i.e., $\gamma <4/3$), the tilt can become extreme at late times and give rise to an effective quintessential equation of state. To establish the connection with phantom cosmology and quintessence, we calculate the effective equation of state in the models under consideration and we determine the future asymptotic behaviour of the tilting models in the fluid frame variables using the boost formulae. We also discuss spatially inhomogeneous models and tilting spatially homogeneous models with a cosmological constant.

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• Dipole Cosmology: The Copernican Paradigm Beyond FLRW
• Spherically symmetric Einstein-aether perfect fluid models
• Static Spherically Symmetric Einstein-aether models II: Integrability and the Modified Tolman-Oppenheimer-Volkoff approach
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• Late-time behaviour of the tilted Bianchi type VIh models
• Kinematic and Weyl singularities
• Late-time behaviour of the tilted Bianchi type VI${}_{-1/9}$ models
• Tilt and phantom cosmology
• Big Bang in Dipole Cosmology
• Properties of kinematic singularities
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• Cosmology: a bird's eye view
• Einstein-aether models III: conformally static metrics, perfect fluid and scalar fields
• Cosmic microwave background limits on spatially homogeneous cosmological models with dark energy
• Mixmaster Fluids Near the Big Bang
• Tilt in quadratic gravity
• Report on GRG18, Session A3, Mathematical Studies of the Field Equations