Inflating without a flat potential: Viscous inflation (original) (raw)
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In this paper, we investigate inhomogeneous viscous fluid cosmology for inflation. Several toy models are presented in the attempt to analyze how inflation can be realized according with cosmological data by making use of an inhomogeneous EoS parameter for the fluid and/or by introducing a viscosity to have a graceful exit from inflation. The results will be compared with the ones of scalar field representation and discussed. We will pay attention on the possibility to recover the reheating and therefore the Friedmann universe. *
Viscous coupled fluids in inflationary cosmology
Journal of Experimental and Theoretical Physics, 2016
We consider the inflation produced by two coupled fluids in the flat Friedmann-Robertson-Walker universe. Different cosmological models for describing inflation by use of an inhomogeneous equation of state for the fluid are investigated. The gravitational equations for energy and matter are solved, and analytic representations for the Hubble parameter and the energy density are obtained. Corrections in the energy density for matter inducing the inflation and the coupling with energy are discussed. We analyze the description of inflation induced by non-constant equation-of-state parameters from fluid viscosity. The correspondence between the spectral index and the tensor-to-scalar ratio recently observed by the Planck satellite is considered.
Inflationary universe in terms of a van der Waals viscous fluid
International Journal of Geometric Methods in Modern Physics, 2017
The inflationary expansion of our early-time universe is considered in terms of the van der Waals equation, as equation of state for the cosmic fluid, where a bulk viscosity contribution is assumed to be present. The corresponding gravitational equations for the energy density in a homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker universe are solved, and an analytic expression for the scale factor is obtained. Attention is paid, specifically, to the role of the viscosity term in the accelerated expansion; the values of the slow-roll parameters, the spectral index, and the tensor-to-scalar ratio for the van der Waals model are calculated and compared with the most recent astronomical data from the Planck satellite. By imposing reasonable restrictions on the parameters of the van der Waals equation, in the presence of viscosity, it is shown to be possible for this model to comply quite precisely with the observational data. One can therefore conclude that the inclusion of...
Warm inflation with bulk viscous pressure for different solutions of an anisotropic universe
2021
We study a warm inflationary model for different expansions assuming an anisotropic universe described by Bianchi I metric. The universe is filled with a scalar field or inflaton, radiation, and bulk viscous pressure. We carry out the inflationary analysis for different solutions of such universe in two different cases of the bulk viscosity coefficient ξ and the dissipation coefficient Γ as constant and variable parameters, respectively. We compare the obtained results with the recent observations, in order to find the observational constraints on the parameters space of the models. Moreover, we attempt to present a better judgment among the considered models by calculation of the non-linear parameter fNL describing the non-Gaussianity property of the models. Additionally, we investigate the warm inflationary models with viscous pressure from the Weak Gravity Conjecture approach, considering the swampland criteria.
2017
In this thesis, we investigate new models of inflation induced by fluids different to standard matter and radiation at the cosmological level. Starting from its historical background, we introduce inflation with the scalar field description. We study trace-anomaly driven inflation and its extended version in F(R) gravity as the most promising inflationary scenario. We compare the results with recent observational data taken by the PLANCK satellite. Further, the fluid description of inflation is introduced and we provide an approach to derive observational parameters from a given equation of state (EoS) for a fluid. Two special types of fluids are investigated in which the EoS has an exponential and power series forms, respectively. We try to fit the parameters in order to produce viable inflation and compare the results with observations. Viscous fluid models are also mentioned, and we show how trace-anomaly driven inflation can be expressed in the fluid description.
BULK VISCOSITY IMPACT ON THE SCENARIO OF WARM INFLATION
The Eleventh Marcel Grossmann Meeting - On Recent Developments in Theoretical and Experimental General Relativity, Gravitation and Relativistic Field Theories - Proceedings of the MG11 Meeting on General Relativity, 2008
The decay of the inflaton into radiation and particles during the slow-roll suggests that these may interact with each other and that the latter may also decay into subproducts before inflation is completed. As a consequence, the fluid is no longer perfect and a nonnegligible bulk viscosity necessarily sets in. We write the corresponding equations as an autonomous system and study the asymptotic behavior, the conditions for the existence of scaling solutions, and show that the late time effect of fluid dissipation alleviates the depletion of matter and increases the duration of inflation.
Constraints on inflationary solutions in the presence of shear and bulk viscosity
General Relativity and Gravitation, 1995
Inflationary models and their claim to solve many of the outstanding problems in cosmology have been the subject of a great deal of debate over the last few years. A major sticking point has been the lack of both good observational and theoretical arguments to single out one particular model out of the many that solve these problems. Here we examine the degree of restrictiveness on the dynamical relationship between the cosmological scale factor and the inflation driving self-interaction potential of a minimally coupled scalar field, imposed by the condition that the scalar field is required to be real during a classical regime (the reality condition). We systematically look at the effects of this constraint on many of the inflationary models found in the literature within the FLRW framework, and also look at what happens when physically motivated perturbations such as shear and bulk viscosity are introduced. We find that in many cases, either the models are totally excluded or the reality condition gives rise to constraints on the scale factor and on the various parameters of the model.
Inflation in terms of a viscous van der Waals coupled fluid
International Journal of Geometric Methods in Modern Physics
We propose to describe the acceleration of the universe by introducing a model of two coupled fluids. We focus on the accelerated expansion at the early stages. The inflationary expansion is described in terms of a van der Waals equation of state for the cosmic fluid, when account is taken of bulk viscosity. We assume that there is a weak interaction between the van der Waals fluid and the second component (matter). The gravitational equations for the energy densities of the two components are solved for a homogeneous and isotropic Friedmann–Robertson–Walker (FRW) universe, and analytic expressions for the Hubble parameter are obtained. The slow-roll parameters, the spectral index, and the tensor-to-scalar ratio are calculated and compared with the most recent astronomical data from the Planck satellite. Given reasonable restriction on the parameters, the agreement with observations is favorable.