Abstract
We consider a warm inflationary scenario in which the two major fluid components of the early Universe, the scalar field and the radiation fluid, evolve with distinct four-velocities. This cosmological configuration is equivalent to a single anisotropic fluid, expanding with a four-velocity that is a combination of the two fluid four-velocities. Due to the presence of anisotropies the overall cosmological evolution is also anisotropic. We obtain the gravitational field equations of the non-comoving scalar field–radiation mixture for a Bianchi Type I geometry. By assuming the decay of the scalar field, accompanied by a corresponding radiation generation, we formulate the basic equations of the warm inflationary model in the presence of two non-comoving components. By adopting the slow-roll approximation the theoretical predictions of the warm inflationary scenario with non-comoving scalar field and radiation fluid are compared in detail with the observational data obtained by the Planck satellite in both weak dissipation and strong dissipation limits, and constraints on the free parameters of the model are obtained. The functional forms of the scalar field potentials compatible with the non-comoving nature of warm inflation are also obtained.
Highlights
The Planck data confirm the foundations of the CDM ( Cold Dark Matter) model
The main material composition of the Universe can be reduced to two components: dark energy and dark matter, respectively, [8,9]
The observed late-time cosmic acceleration of the Universe [10,11,12,13] can be successfully explained by introducing either a fundamental cosmological constant [14], which would represent an intrinsic curvature of spacetime, or a dark energy, a hypothetical fluid component in the form of a zero-point-energy that pervades the whole Universe, which would mimic a cosmological constant [8,9,15,16,17,18,19]
Summary
By varying the total action with respect to the metric and the scalar field φ, we obtain the energy–momentum tensor of the system as T μν Lφ gμν. If the scalar field and the photon gas have the same four-velocity, the thermodynamic parameters of the scalar field–radiation two-fluid system are obtained a simple addition of the enthalpies and the pressures of the individual components For such a physical system one can always introduce a comoving frame, in which the components of the fourvelocity are wμ = (1, 0, 0, 0), with the components of the total energy–momentum tensor of the two fluids given by T00 = ρφ + ρrad δ00, and Tii = − pφ + prad δii , i = 1, 2, 3, no summation over i. In our analysis of the warm inflationary scenarios in non-comoving frames we will assume that the energy density and the pressure of the scalar field satisfy the condition ρφ + pφ ≥ 0, that is, the scalar field cannot be interpreted as a simple cosmological constant
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