Related papers: Causal Bulk Viscous Dissipative Isotropic Cosmolog…
We provide a detailed analysis of Friedmann-Robertson-Walker universes in a wide range of scalar-tensor theories of gravity. We apply solution-generating methods to three parametrised classes of scalar-tensor theory which lead naturally to…
The Hubble constant problem is the discrepancy between different measurements of the Hubble constant in different scales. We show that this problem can be resolved within the general relativistic framework of the perturbation theory in the…
We consider a cosmological model dominated by bulk viscous matter with total bulk viscosity coefficient proportional to the velocity and acceleration of the expansion of the universe in such a way that…
In this paper we suppose that the cosmological constant will change when the universe expends. For a general consideration, the cosmological constant is assumed to be a function of scale factor and Hubble constant. According to the ADM…
We propose a mechanism for generating an inflationary phase in the early universe without resorting to any type of scalar field(s). Instead, this accelerated expansion is driven by a dynamical "cosmological constant" in the framework of…
We often find in the literature solutions to the Friedmann and fluid equations for simple cosmological models during the matter, radiation or cosmological constant dominated epochs. However no solutions appear for the inflationary era…
In this manuscript, we show that three fundamental building blocks are supporting the Cosmological Principle. The first of them states that there is a special frame in the universe where the spatial geometry is intrinsically homogeneous and…
The gravitino problem is revisited in the framework of cosmological models in which the primordial cosmic matter is described by a relativistic imperfect fluid. Dissipative effects (or bulk viscosity effects) arise owing to the different…
A quantum expansion parameter, analogous to the Hubble parameter in cosmology, is defined for a free particle quantum wavefunction. By considering the universe as an initial single Gaussian quantum wavepacket whose mass is that of…
The Hubble parameter is kinematically defined in terms of the positions and velocities of all particles in a universe which may or may not be finite. This definition is set equal to the Hubble parameter as defined in the Friedman-Lema\^itre…
In this paper, we have assumed a flat Friedmann-Lemaitr\'e-Robertson-Walker universe endowed with a general form of dissipation. The source of dissipation is considered to be a bulk viscous pressure $\Pi$ which leads to an adiabatic…
Basing on the increasing evidence for the cosmological relevance of the local Hubble flow, we consider a simple analytical cosmological model for the Local Universe. This is a non-Friedmann model with a non-uniform static space-time. The…
In the present work, we study for the first time a scale--dependent gravitational theory in a cosmological context in a matter--dominated era. In particular, starting from the Einstein Hilbert action with cosmological constant assuming…
We study solutions of the Wheeler-DeWitt equation corresponding to an S-modular invariant N=1 supergravity model and a closed homogeneous and isotropic Friedmann-Robertson-Walker spacetime. The issues of inflation and of the cosmological…
This study combines theoretical advancements with observational limitations to investigate the cosmological implications of a bulk viscous modified Chaplygin gas (MCG) in a Friedmann--Robertson--Walker (FRW) in (3+1) dimensional spacetime…
In this paper, we have presented bulk viscous cosmological model of the universe in the modified gravity theory in which the Lagragian of the gravitational action contains a general function $f(R, T) $, where $R$ and $T$ denote the…
In this paper, we explore a theoretical and observational study of the presence of viscosity in the Unimodular Gravity formalism, a pioneering approach that, to the best of our knowledge, has not been previously explored in this context.…
We point out that the standard formulation of the cosmological constant problem itself is problematic since it is trying to apply the very large scale homogeneous cosmological model to very small (Planck) scale phenomenon. At small scales,…
The effect of a time dependent cosmological constant is considered in a family of scalar tensor theories. Friedmann-Robertson-Walker cosmological models for vacumm and perfect fluid matter are found. They have a linear expansion factor, the…
Theories with ingredients like the Higgs mechanism, gravitons, and inflaton fields rejuvenate the idea that relativistic kinematics is dynamically emergent. Eternal inflation treats the Hubble constant H as depending on location.…