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Register a new user$Lambda$-CDM type Heckmann - Suchuking model and union 2.1 compilation
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Added by
Gopi Kant Goswami Dr
Publication date
2015
fields
Physics
and research's language is
English
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In this paper, we have investigated $Lambda$CDM type cosmological model in Heckmann-Schucking space-time, by using 287 high red shift ($ .3 leq z leq 1.4$ ) SN Ia data of observed absolute magnitude along with their possible error from Union 2.1 compilation. We have used $chi^{2}$ test to compare Union 2.1 compilation observed data and corresponding theoretical values of apparent magnitude $(m)$. It is found that the best fit value for $(Omega_{m})_0$, $(Omega_{Lambda})_0$ and $(Omega_{sigma})_0$ are $0.2940$, $0.7058$ and $0.0002$ respectively and the derived model represents the features of accelerating universe which is consistent with recent astrophysical observations.
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In the present work we have searched the existence of the late time acceleration of the universe with string fluid as source of matter in anisotropic Heckmann-Suchking space-time by using 287 high red shift $(0.3 leq zleq 1.4)$ SN Ia data of observed absolute magnitude along with their possible error from Union 2.1 compilation. It is found that the best fit values for $(Omega_{m})_{0}$, $(Omega_{Lambda})_{0}$, $(Omega_{sigma})_{0}$ and $(q)_{0}$ are 0.2820, 0.7177, 0.0002 $&$ -0.5793 respectively. Several physical aspects and geometrical properties of the model are discussed in detail.
The recent robust and homogeneous analysis of the worlds supernova distance-redshift data, together with cosmic microwave background and baryon acoustic oscillation data, provides a powerful tool for constraining cosmological models. Here we examine particular classes of scalar field, modified gravity, and phenomenological models to assess whether they are consistent with observations even when their behavior deviates from the cosmological constant Lambda. Some models have tension with the data, while others survive only by approaching the cosmological constant, and a couple are statistically favored over LCDM. Dark energy described by two equation of state parameters has considerable phase space to avoid Lambda and next generation data will be required to constrain such physics.
We present an explicit detailed theoretical and observational investigation of an anisotropic massive Brans-Dicke (BD) gravity extension of the standard $Lambda$CDM model, wherein the extension is characterized by two additional degrees of freedom; the BD parameter, $omega$, and the present day density parameter corresponding to the shear scalar, $Omega_{sigma^2,0}$. The BD parameter, determining the deviation from general relativity (GR), by alone characterizes both the dynamics of the effective dark energy (DE) and the redshift dependence of the shear scalar. These two affect each other depending on $omega$, namely, the shear scalar contributes to the dynamics of the effective DE, and its anisotropic stress --which does not exist in scalar field models of DE within GR-- controls the dynamics of the shear scalar deviating from the usual $propto(1+z)^6$ form in GR. We mainly confine the current work to non-negative $omega$ values as it is the right sign --theoretically and observationally-- for investigating the model as a correction to the $Lambda$CDM. By considering the current cosmological observations, we find that $omegagtrsim 250$, $Omega_{sigma^2,0}lesssim 10^{-23}$ and the contribution of the anisotropy of the effective DE to this value is insignificant. We conclude that the simplest anisotropic massive BD gravity extension of the standard $Lambda$CDM model exhibits no significant deviations from it all the way to the Big Bang Nucleosynthesis. We also point out the interesting features of the model in the case of negative $omega$ values; for instance, the constraints on $Omega_{sigma^2,0}$ could be relaxed considerably, the values of $omegasim-1$ (relevant to string theories) predict dramatically different dynamics for the expansion anisotropy.
We show that a cosmology driven by gravitationally induced particle production of all non-relativistic species existing in the present Universe mimics exactly the observed flat accelerating $Lambda$CDM cosmology with just one dynamical free parameter. This kind of scenario includes the creation cold dark matter (CCDM) model [Lima, Jesus & Oliveira, JCAP 011(2010)027] as a particular case and also provides a natural reduction of the dark sector since the vacuum component is not needed to accelerate the Universe. The new cosmic scenario is equivalent to $Lambda$CDM both at the background and perturbative levels and the associated creation process is also in agreement with the universality of the gravitational interaction and equivalence principle. Implicitly, it also suggests that the present day astronomical observations cannot be considered the ultimate proof of cosmic vacuum effects in the evolved Universe because $Lambda$CDM may be only an effective cosmology.
This paper treats nonrelativistic matter and a scalar field $phi$ with a monotonically decreasing potential minimally coupled to gravity in flat Friedmann-Lema^{i}tre-Robertson-Walker cosmology. The field equations are reformulated as a three-dimensional dynamical system on an extended compact state space, complemented with cosmographic diagrams. A dynamical systems analysis provides global dynamical results describing possible asymptotic behavior. It is shown that one should impose emph{global and asymptotic} bounds on $lambda=-V^{-1},dV/dphi$ to obtain viable cosmological models that continuously deform $Lambda$CDM cosmology. In particular we introduce a regularized inverse power-law potential as a simple specific example.
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