Exact solutions, finite time singularities and non-singular universe models from a variety of Λ(t) cosmologies

Abstract

Cosmological models with time dependent Λ (read as Λ(t)) have been investigated widely in the literature. Models that solve background dynamics analytically, are of special interest. Additionally, the allowance of past or future singularities at finite cosmic time in a specific model signals for a generic test on its viabilities with the current observations. Following these, in this work we consider a variety of Λ(t) models focusing on their evolutions and singular behaviour. We found that a series of models in this class can be exactly solved when the background universe is described by a spatially flat Friedmann-Lemaître-Robertson-Walker (FLRW) line element. The solutions in terms of the scale factor of the FLRW universe offer different universe models, such as power law expansion, oscillating, and the singularity free universe as well. However, we also noticed that a large number of models in this series permits past or future cosmological singularities at finite cosmic time. At last we close the work with a note that the avoidance of future singularities is possible for certain models under some specific restrictions.PACS numbers: 98.80.-k, 95.36.+x

Dark calling dark: interaction in the dark sector in presence of neutrino properties after Planck CMB final release

“…We can only approximate the interaction function Q only through the theoretical arguments and consistent observational data. It is assumed that the interaction between the dark components may appear from some effective field theory [82], disformal coupling [83,84], decay of vacuum energy [85,86,87,88], or something else. However, it is extremely difficult, and/or at some level it is even unfeasible to test the interaction models from the action principle.…”

Dynamics of Einstein–Aether scalar field cosmology

“…which looks like the particle creation, bulk viscosity or varying vacuum theories [60][61][62][63][64][65][66]. Positive values of B φ indicate particle annihilation while negative values of B φ indicate particle creation.…”

Similarity solutions for the Wheeler–DeWitt equation in $$f\left( R\right) $$-cosmology

“…Some theories which belong to that class of models are the: f (R)-gravity in the metric formalism [7], f R -gravity in the Palatini formalism [8], f (G)-Gauss Bonnet theory [9], while in the Teleparallel formalism of gravity the f (T ) −theory has been widely studied the last decade [10][11][12][13]. For other modified theories which belong to that class we referee the reader to [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] and references therein.…”