Abstract:
In this thesis, we chose VMCG with a specific bulk viscosity pressure as a toy
model for our universe to explore its behavior at present time, when fitted to recent
observational data, and at late time to check whether it suffers from singularities or not.
The Eos parameters are constrained for a suitable model that describes the current universe.
We also evaluate the evolution of the state and deceleration parameters at present and early
universe and determine their present values to deduce if the model is consistent or not with
observation data and theoretical predictions. The values are compared to those of other well
accepted models. Then, we probe the dynamical behavior of our toy model at early and late
time in the LQC framework especially as the model suffers from the Big Bang singularity.
The model is found suitable to describe the current universe with consistent present values of
both state and deceleration parameters ∈ (−0.76, −0.74) , ∈ (−0.60, −0.57). At
large scale, the VMCG has no future singularities and its equation of state is nearly equivalent
to cosmological constant ( = -1). The sound speed takes a constant value different from
zero as a difference between a dynamical fluid model and an inert cosmological constant
model. The VMCG discussed here reproduces the main results of the standard model without
assuming a priori the existence of cosmological constant, the problems related to fine-tuning
and coincidence problems are solved and the value of the redshift where ( ≈ ) for
both
= 0.01and = 0.0001 is z = 0.75.
At LQC background and at large scale the results found are the same as those of classical
background and at small scale the Big Bang singularity problem is solved and replaced by a
bounce, at large scale the stability of the model does not depend on the EoS parameter and
VMCG universe solutions depend only on .
