Reacting fluids in the expanding universe: a new mechanism for entropy production (original) (raw)
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Dissipative Processes in the Early Universe: Bulk Viscosity
Arxiv preprint arXiv:0911.4105, 2009
In this talk, we discuss one of the dissipative processes which likely take place in the Early Universe. We assume that the matter filling the isotropic and homogeneous background is to be described by a relativistic viscous fluid characterized by an ultra-relativistic equation of state and finite bulk viscosity deduced from recent lattice QCD calculations and heavy-ion collisions experiments. We concentrate our treatment to bulk viscosity as one of the essential dissipative processes in the rapidly expanding Early Universe and deduce the dependence of the scale factor and Hubble parameter on the comoving time t. We find that both scale factor and Hubble parameter are finite at t = 0, revering to absence of singularity. We also find that their evolution apparently differs from the one resulting in when assuming that the background matter is an ideal and non-viscous fluid.
Cosmological particle production and generalized thermodynamic equilibrium
Physical Review D, 1998
With the help of a conformal, timelike Killing-vector we define generalized equilibrium states for cosmological fluids with particle production. For massless particles the generalized equilibrium conditions require the production rate to vanish and the well known "global" equilibrium of standard relativistic thermodynamics is recovered as a limiting case. The equivalence between the creation rate for particles with nonzero mass and an effective viscous fluid pressure follows as a consequence of the generalized equilibrium properties. The implications of this equivalence for the cosmological dynamics are discussed, including the possibility of a power-law inflationary behaviour. For a simple gas a microscopic derivation for such kind of equilibrium is given on the basis of relativistic kinetic theory.
Self-interacting cosmic fluids: Particle production, causal evolution, and vacuum decay
1999
We discuss two different realizations of a ``deflationary'' scenario of the early universe which imply a smooth transition from an initial de Sitter stage to a subsequent radiation-dominated FLRW period. Thermodynamically, this transition is a non-equilibrium process which may also be interpreted as the decay of an initial cosmic vacuum into relativistic matter.
Thermodynamics of viscous matter and radiation in the early universe
Canadian Journal of Physics, 2012
Assuming that the background geometry is filled with a free gas consisting of matter and radiation and that no phase transitions are occurring in the early universe, we discuss the thermodynamics of this closed system using classical approaches. We find that essential cosmological quantities, such as the Hubble parameter H, scale factor a, and curvature parameter k, can be derived from this simple model. On one hand, it obeys the laws of thermodynamics entirely. On the other hand, the results are compatible with the Friedmann–Lemaitre–Robertson–Walker model and the Einstein field equations. The inclusion of a finite bulk viscosity coefficient derives important changes in all of these cosmological quantities. The thermodynamics of the viscous universe is studied and a conservation law is found. Accordingly, our picture of the evolution of the early universe and its astrophysical consequences seems to be the subject of radical revision. We find that the parameter k, for instance, stro...
Physical Review D, 1996
The full causal Müller-Israel-Stewart (MIS) theory of dissipative processes in relativistic fluids is applied to a flat, homogeneous and isotropic universe with bulk viscosity. It is clarified in which sense the so called truncated version is a reasonable limiting case of the full theory. The possibility of bulk viscosity driven inflationary solutions of the full theory is discussed. As long as the particle number is conserved almost all these solutions exhibit an exponential increase of the temperature. Assuming that the bulk viscous pressure of the MIS theory may also be interpreted as an effective description for particle production processes, the thermodynamical behaviour of the Universe changes considerably. In the latter case the temperature increases at a lower rate or may remain constant during a hypothetical de Sitter stage, accompanied by a substantial growth of the comoving entropy.
‘Understanding’ cosmological bulk viscosity
Monthly Notices of the Royal Astronomical Society, 1996
A universe consisting of two interacting perfect fluids with the same 4-velocity is considered. A heuristic mean free time argument is used to show that the system as a whole cannot also be perfect, but necessarily implies a non-vanishing bulk viscosity. A new formula for the bulk viscosity is derived and compared with corresponding results of radiative hydrogynamics.
Bulk Viscosity and Particle Creation in the Inflationary Cosmology
We study particle creation in the presence of bulk viscosity of cosmic fluid in the early universe within the framework of open thermodynamical systems. Since the first-order theory of non-equilibrium thermodynamics is non-causal and unstable, we try to solve the bulk viscosity equation of the cosmic fluid with particle creation through the full causal theory. By adopting an appropriate function for particle creation rate of "Creation of Cold Dark Matter" model, we obtain analytical solutions which do not suffer from the initial singularity and are in agreement with equivalent solutions of Lambda-CDM model. We constrain the free parameter of particle creation in our model based on recent Planck data. It is also found that the inflationary solution is driven by bulk viscosity with or without particle creation.
Bulk viscous cosmology: Statefinder and entropy
Physics Letters B, 2006
The statefinder diagnostic pair is adopted to differentiate viscous cosmology models and it is found that the trajectories of these viscous cosmology models on the statefinder pair s − r plane are quite different from those of the corresponding non-viscous cases. Particularly for the quiessence model, the singular properties of state parameter w = −1 are obviously demonstrated on the statefinder diagnostic pair planes. We then discuss the entropy of the viscous / dissipative cosmology system which may be more practical to describe the present cosmic observations as the perfect fluid is just a global approximation to the complicated cosmic media in current universe evolution. When the bulk viscosity takes the form of ζ = ζ1ȧ/a(ζ1 is constant), the relationship between the entropy S and the redshift z is explicitly given out. We find that the entropy of the viscous cosmology is always increasing and consistent with the thermodynamics arrow of time for the universe evolution. With the parameter constraints from fitting to the 157 gold data of supernova observations, it is demonstrated that this viscous cosmology model is rather well consistent to the observational data at the lower redshifts, and together with the diagnostic statefinder pair analysis it is concluded that the viscous cosmic models tend to the favored ΛCDM model in the later cosmic evolution, agreeable to lots of cosmological simulation results, especially to the fact of confidently observed current accelerating cosmic expansion.
Thermodynamic aspects of entropic cosmology with viscosity
International Journal of Modern Physics D, 2020
We describe the evolution of the early and late universe from thermodynamic considerations, using the generalized nonextensive Tsallis entropy with a variable exponent. A new element in our analysis is the inclusion of a bulk viscosity in the description of the cosmic fluid. Using the generalized Friedmann equation, a description of the early and the late universe is obtained.
Entropy production in an expanding universe
Physics Letters B, 1985
We consider an interacting scalar field in a time-dependent background and estimate dissipative effects due to particle production and/or interactions of the field with a heat bath using techniques of thermo field dynamics. Assuming the system is in near-thermal equilibrium, a general expression for the source of friction is presented. Applying the result to an expanding universe, the effective equation of motion for the classical background is obtained and implications are discussed.