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Specific internal self-interactions in gaseous cosmic fluids are shown to give rise to effective negative pressures which may violate the strong energy condition. On this basis we discuss the transition from an initial de Sitter phase to a subsequent Friedmann-Lema^{i}tre-Robertson-Walker period as a non-equilibrium configuration of an ultrarelativistic gas. An accelerated expansion of the present universe is obtained as the consequence of a negative internal friction force which is self-consistently exerted on the non-relativistic cold dark matter (CDM) type microscopic constituents of the cosmic gas.
We study the dynamical properties of tracker quintessence models using a general parametrization of their corresponding potentials, and show that there is a general condition for the appearance of a tracker behavior at early times. Likewise, we deter
Quintessence field is a widely-studied candidate of dark energy. There is tracker solution in quintessence models, in which evolution of the field $phi$ at present times is not sensitive to its initial conditions. When the energy density of dark ener
We show that the cosmological evolution of a scalar field in a potential can be obtained from a renormalisation group equation. The slow roll regime of inflation models is understood in this context as the slow evolution close to a fixed point, descr
We consider several new classes of viable vector field alternatives to the inflaton and quintessence scalar fields. Spatial vector fields are shown to be compatible with the cosmological anisotropy bounds if only slightly displaced from the potential
We examine hilltop quintessence models, in which the scalar field is rolling near a local maximum in the potential, and w is close to -1. We first derive a general equation for the evolution of the scalar field in the limit where w is close to -1. We