Topic
Deceleration parameter
About: Deceleration parameter is a research topic. Over the lifetime, 1776 publications have been published within this topic receiving 89440 citations.
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TL;DR: In this paper, the recent cosmic expansion was investigated by directly reconstructing the deceleration parameter $q(z)$ at recent times with a linear expansion at $z=0$ using the low redshift SNIa and BAO data and the results showed that the observations seem to favor a slowing down of the present cosmic acceleration.
Abstract: We probe the recent cosmic expansion by directly reconstructing the deceleration parameter $q(z)$ at recent times with a linear expansion at $z=0$ using the low redshift SNIa and BAO data. Our results show that the observations seem to favor a slowing down of the present cosmic acceleration. Using only very low redshift SNIa data, for example, those within $z<0.1$ or $0.2$, we find that our Universe may have already entered a decelerating expansion era since a positive $q(0)$ seems to be favored. This result is further supported by a different approach which aims to reconstruct $q(z)$ in the whole redshift region. So, the accelerating cosmic expansion may be just a transient phenomenon.
8 citations
TL;DR: In this article, a spatially homogeneous and anisotropic string cosmological models in the Brans-Dicke theory of gravitation were discussed, where it is assumed that the expansion scalar θ is proportional to the shear scalar σ.
Abstract: We discuss a spatially homogeneous and anisotropic string cosmological models in the Brans–Dicke theory of gravitation. For a spatially homogeneous metric, it is assumed that the expansion scalar θ is proportional to the shear scalar σ. This condition leads to A = kB
m
, where k and m are constants. With these assumptions and also assuming a variable scale factor a = a(t), we find solutions of the Brans–Dicke field equations. Various phenomena like the Big Bang, expanding universe, and shift from anisotropy to isotropy are observed in the model. It can also be seen that in early stage of the evolution of the universe, strings dominate over particles, whereas the universe is dominated by massive strings at the late time. Some physical and geometrical behaviors of the models are also discussed and observed to be in good agreement with the recent observations of SNe la supernovae.
8 citations
TL;DR: In this article, an accelerating model of a flat universe with a linearly varying deceleration parameter (LVDP) was proposed, and the linear time-varying law was applied to generate a model of transition from an early decelerating phase to the current accelerating phase.
Abstract: The
$$f(R,T)$$
theory of gravity is an extended theory of gravity in which the gravitational action contains both the Ricci scalar
$$R$$
and the trace of the energy-momentum tensor
$$T$$
, and hence the cosmological models based on
$$f(R,T)$$
gravity are eligible to describing the late-time acceleration of the present universe. In this paper, we investigate an accelerating model of a flat universe with a linearly varying deceleration parameter (LVDP). We apply the linear time-varying law for the deceleration parameter that generates a model of a transition from an early decelerating phase to the current accelerating phase. We carry out the state-finder and Om(z) analysis, and obtain that the LVDP model has a consistency with the astrophysical observations. We also profoundly discuss a violation of the energy-momentum conservation law in
$$f(R,T)$$
gravity and the dynamic behavior of the model.
8 citations
TL;DR: In this article, the authors studied the solutions of plane-symmetric universe with variable ω in the presence and the absence of magnetic field of energy density ρ B 74, 182.
Abstract: In this paper, we have studied the solutions of plane-symmetric Universe with variable ω in the presence and the absence of magnetic field of energy density ρ
B
. A special law of variation for Hubble’s parameter proposed by Bermann in Nuovo Cimento B 74, 182 (1983) has been utilized to solve the field equations. Some physical and kinematical properties of the models are also discussed.
8 citations
TL;DR: In this article, the authors examined the Kantowski-Sachs space-time in the presence of strange quark matter with the appearance and nonappearance of strings in f(R) gravity.
Abstract: In this paper, we have examined the Kantowski–Sachs space-time in the presence of strange quark matter with the appearance and non-appearance of strings in f(R) gravity. Here, R is the Ricci scalar of the space-time. Exact solutions of the field equations are obtained by considering the following conditions (i) hybrid scale factor, (ii) the proportionality of shear scalar (
$$\sigma$$
) with expansion scalar (
$$\theta$$
) and (iii) power-law between the scalar-on function F(R) and average scale factor a(t). We have investigated some physical and geometrical properties of the models, and their behavior is thoroughly studied with the help of graphical representation.
8 citations