Thermodynamics of Modified Cosmic Chaplygin Gas

We examine the thermodynamic features of an exotic fluid known as modified cosmic Chaplygin gas in the context of homogeneous isotropic universe model. For this purpose, the behavior of physical parameters is discussed that help to analyze nature of the universe. Using specific heat formalism, the validity of third law of thermodynamics is checked. Furthermore, with the help of thermodynamic entities, the thermal equation of state is also discussed. The thermodynamic stability is explored by means of adiabatic, specific heat and isothermal conditions from classical thermodynamics. It is concluded that the considered fluid configuration is thermodynamically stable and expands adiabatically for an appropriate choice of parameters.

Cosmological models for an homogeneous, isotropic universe

The universe is homogeneous and isotropic on sufficiently large scales. The metric which describes such a space-time is derived and it is shown that it is determined by the scale factor a(t) and the parameter k distinguishing between hyperbolic, flat, or spherical 3-spaces. The Friedmann equations, which describe the time evolution of these models, are derived and specific models are discussed.

Qualitative types of cosmological evolution in hydrodynamic models with barotropic equation of state

We study solutions of the Friedmann equations in case of the homogeneous isotropic Universe filled with a perfect fluid. The main points concern the monotony properties of the solutions, the possibility to extend the solutions on all times and occurrence of singularities. We present a qualitative classification of all possible solutions in case of the general smooth barotropic equation of state of the fluid, provided the speed of sound is finite. The list of possible scenarios includes analogues of the "Big Rip" in the future and/or in the past as well as singularity free solutions and oscillating Universes. Extensions of the results to the multicomponent fluids are discussed.

A MINIMAL MODEL FOR DILATONIC GRAVITY

We study a new minimal scalar–tensor model of gravity with Brans–Dicke factor ω(Φ)≡0 and cosmological factor Π(Φ). The constraints on Π(Φ) from known gravitational experiments are derived. We show that almost any time evolution of the scale factor in a homogeneous isotropic Universe can be obtained via a properly chosen Π(Φ) and discuss the general properties of models of this type.