Phantom cosmology without Big Rip singularity

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Various cosmological models in frames of F (T ) gravity are considered. The general scheme of constructing effective dark energy models with various evolution is presented. It is showed that these models in principle are compatible with ΛCDM model. The dynamics of universe governed by F (T ) gravity can mimics ΛCDM evolution in past but declines from it in a future. We also construct some dark energy models with the "real" (non-effective) equation-of-state parameter w such that w ≤ −1. It is showed that in F (T ) gravity the Universe filled phantom field not necessarily ends its existence in singularity. There are two possible mechanisms permitting the final singularity. Firstly due to the nonlinear dependence between energy density and H 2 (H is the Hubble parameter) the universe can expands not so fast as in the general relativity and in fact Little Rip regime take place instead Big Rip. We also considered the models with possible bounce in future. In these models the universe expansion can mimics the dynamics with future singularity but due to bounce in future universe begin contracts.

“…The various possibilities of universe evolution in frames of usual FRLW cosmology are described in detail [48]. Here we note the some features which can take place in F (T ) background.…”

Section: Dark Energy Cosmology In F (T ) Gravitymentioning

confidence: 99%

Effective dark energy models and dark energy models with bounce in frames of F(T) gravity

Astashenok

2014

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“…Interesting alternatives to the ΛCDM model are models in which the dark energy density tends asymptotically to a constant value (an "effective cosmological constant" [16]). One should remark that if the value of this "effective cosmological constant" is sufficiently large (for example, if Λ ef f ∼ 1 in Planck units) a possibility of disappearance of bound structures due to the enormous acceleration of the universe still remains.…”

Section: Comparison Of Dark Energy In Frw-and Brane-cosmologymentioning

confidence: 99%

“…For a universe filled with phantom energy there are many possible new scenarios for the end of such universe, among which the most typical cases are those of a Big Rip singularity [7,[9][10][11][12] and of a sudden future singularity [13]. However, a final evolution without singularities is also possible: if the parameter w asymptotically tends to −1, and the energy density increases with time or remains constant, no finite-time future singularity will be ever formed [14][15][16][17][18], also, if the universe starts to decelerate in the far future. In any case, if the energy density grows up to some threshold value, the disintegration of any bound structure will eventually occur, in a way quite similar to the case of the Big Rip singularity, but this may only happen faraway in the future evolution.…”

Section: Introductionmentioning

confidence: 99%

Brane cosmology from observational surveys and its comparison with standard FRW cosmology

Astashenok

Elizalde

Haro

et al. 2013

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Several dark energy models on the brane are investigated. They are compared with corresponding theories in the frame of 4d Friedmann-Robertson-Walker cosmology. To constrain the parameters of the models considered, recent observational data, including SNIa apparent magnitude measurements, baryon acoustic oscillation results, Hubble parameter evolution data and matter density perturbations are used. Explicit formulas of the so-called state-finder parameters in teleparallel theories are obtained that could be useful to test these models and to establish a link between Loop Quantum Cosmology and Brane Cosmology. It is concluded that a joint analysis as the one developed here allows to estimate, in a very convenient way, possible deviation of the real universe cosmology from the standard Friedmann-Robertson-Walker one.

“…It is also shown recently that EU model can be successfully implemented in Brane world gravity [20,21], Brans-Dicke theory [22]. A number of cosmological models are obtained with different cosmological fluids and fields [14,[23][24][25][26] where initial singularity problem is addressed. Mukherjee et al [13] obtained an emergent universe model in the framework of GTR with a polytropic equation of state (EoS) given by…”

Section: Introductionmentioning

confidence: 99%

Observational constraints on EoS parameters of emergent universe

Paul

Thakur²

2017

Abstract. We investigate emergent universe model using recent observational data for the background tests as well as for the growth tests. The background test data comprises of Hubble data, Baryon Acoustic Oscillation (BAO) data, cosmic microwave background (CMB) shift data, Union compilation data. The observational growth data are obtained from Wiggle-Z measurements and rms mass fluctuations data from Lyman-α measurements at different red shifts. The flat emergent universe model obtained by Mukherjee et. al. is permitted with a non-linear equation of state (in short, EoS) (p = Aρ − Bρ 1 2 ), where A and B are constants. The observed cosmological data are used here to estimate the range of allowed values of EoS parameters numerically. The best-fit values of the EoS and growth parameters are determined making use of chi-square minimization technique. The analysis is carried out here considering the Wang-Steinhardt ansatz for growth index (γ) and growth function (f defined as f = Ω γ m (a)). Subsequently, the best-fit values of the EoS parameters are used to study the evolution of the growth function f , growth index γ, state parameter ω with red shift parameter z. The present value of the parameters, namely, f , γ, ω, Ω m are also estimated. The late accelerating phase of the universe in the model is accommodated satisfactorily.