Wet Dark Fluid Cosmological Model in Barber Self-Creation Theory of Gravitation

This paper investigates a Bianchi type VIII cosmological model with wet dark fluid in Barber self-creation theory of gravitation. To get the determinate model of the Universe, we have assumed the relationship between metric coefficients R and S. Also, the behavior of the model in the radiation Universe and the physical implications of the model are discussed in detail.

Study of cosmic models in f(R,T) gravity with tilted observers

In this work, we have studied LRS Bianchi type I cosmological models in [Formula: see text] gravity with tilted observers, where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of the stress energy tensor. We have explored a tilted model and determined the solutions of the field equations by assuming special law of variation of Hubble’s parameter, proposed by Berman (1983) that yields constant deceleration parameter. In this scenario, we have used the equation of state [Formula: see text] and power law of velocity to describe the different anisotropic physical models such as Dust Universe, Radiation Universe, Hard Universe and Zedovich Universe. We have discussed graphical presentation of all parameters of the derived models with the help of MATLAB. Some physical and geometrical aspects of the models are also discussed.

Investigating cosmology with equation of state

The aim of this paper is to investigate the field equations of modified [Formula: see text] theory of gravity, where R and [Formula: see text] represent the Ricci scalar and scalar potential, respectively. We consider the Friedmann–Robertson–Walker space–time for finding some exact solutions by using different values of equation of state parameter. In this regard, different possibilities of the exact solutions have been discussed for dust universe, radiation universe, ultra-relativistic universe, sub-relativistic universe, stiff universe, and dark energy universe. Mainly power law and exponential forms of the scale factor are chosen for the analysis.

COSMOLOGICAL QUINTESSENCE ACCRETION ONTO PRIMORDIAL BLACK HOLES: CONDITIONS FOR THEIR GROWTH TO THE SUPERMASSIVE SCALE

In this work we revisit the growth of small primordial black holes (PBHs) immersed in a quintessential field and/or radiation to the supermassive black hole (SMBHs) scale. We show the difficulties of scenarios in which such huge growth is possible. For that purpose we evaluated analytical solutions of the differential equations (describing mass evolution) and point out the strong fine tuning for the conclusions. The timescale for growth in a model with a constant quintessence flux is calculated and we show that it is much bigger than the Hubble time. The fractional gain of the mass is further evaluated in other forms, including quintessence and/or radiation. We calculate the cosmological density Ω due to quintessence necessary to grow BHs to the supermassive range and show it to be much bigger than one. We also describe the set of complete equations analyzing the evolution of the BH + quintessence universe, showing some interesting effects such the quenching of the BH mass growth due to the evolution of the background energy. Additional constraints obtained by using the Holographic Bound are also described. The general equilibrium conditions for evaporating/accreting black holes evolving in a quintessence/radiation universe are discussed in Appendix.

LRS BIANCHI TYPE-I COSMOLOGICAL MODELS IN BARBER'S SECOND SELF CREATION THEORY

Barber's second self creation theory with perfect fluid source for an LRS Bianchi type-I metric is considered using deceleration parameter to be constant where the metric potentials are taken as functions of x and t. In particular, some exact solutions have also been obtained for the vacuum universe, Zel'dovich universe and radiation universe. Some physical properties of the models are also discussed.

A KINEMATIC DESCRIPTION OF THE EXPANSION OF THE UNIVERSE

A kinematic expression for the Hubble parameter H is derived which defines it directly in terms of the positions and velocities of all existing mass particles. The derivation is simply based on the concept that the numerical value of H at any instant of time is determined solely by particle positions and velocities that exist at that instant, and it is only indirectly affected by gravity through its actions on particles which change the positions and velocities. This definition of H does not depend on the motion of photons because the motion of a photon in a distant galaxy is determined by H as it moves with a constant velocity in the galaxy’s inertial system at rest in the Hubble drift. The kinematic definition of H is shown to be identical to the conventional expression H=Ṙ/R. Under general conditions it behaves in the usual manner. But in the case when all matter is located in a small volume of space, such as that which could have occurred at the time of origin of the universe, there exists for a brief time a kinematic repulsion which acts in addition to the usual gravitational attraction that is described in the standard solution of relativity. The repulsion could be strong enough to overcome gravitation and cause even a static universe to quickly evolve into an expanding one. In the case of an initially pure and static radiation universe that subsequently expands and creates all matter during the expansion, the kinematically defined H allows matter to be created in clusters at a very early time within a highly uniform background of radiation.