With due consideration of reasonable cosmological assumptions within the limit of the present cosmological scenario, we have analysed a spherically symmetric metric in 5D setting within the framework of Lyra manifold. The model universe is predicted to be a DE model, dominated by vacuum energy. The model represents an oscillating model, each cycle evolving with a big bang and ending at a big crunch, undergoing a series of bounces. The universe is isotropic and undergoes super-exponential expansion. The value of Hubble's parameter is measured to be $H=67.0691$ which is very close to $H_0=67.36\pm0.54kms^{-1}Mpc^{-1}$, the value estimated by the latest Planck 2018 result. A detailed discussion on the cosmological parameters obtained is also presented with graphs.
We investigate the cosmological dynamics of interacting Logarithmic Entropy Corrected Holographic Dark Energy model with Cold Dark Matter. Fixed points are determined and their corresponding cosmological models are presented. Moreover, the dynamical properties of these fixed points are derived.
We have explored cold dark matter and holographic dark energy cosmological models with big rip singularity. To obtain the solution of the field equation, we have supposed that scalar expansion $θ$ is proportional to shear scalar $σ^2 $ which leads to $p_1=(p_2) ^n $, where $A_1 $, $A_2$ are metric potentials and $ n$ is constant. Big bang and Big rip singularity are investigated and analyzed the state-finder parameter. The physical and geometrical parameters of the universe are explained.
We consider the cosmological system with two interacting fluids: dark energy and dark matter, in a homogeneous and isotropic universe with dissipation. The modified gravitational equation for dark matter is solved. The analytic representations for the Little Rip, the Pseudo Rip, and the bounce cosmology models with dissipation are obtained in terms of the thermodynamic parameters in the equation of state. We analyze the corrections in the energy density for dark matter, in view of the dissipative processes and the coupling with dark energy.
Based on Wheeler-DeWitt equation derived from general relativity, it had been found that only dark energy can lead to a normalizable cosmological wave function. It is shown in the present work that, for dRGT gravity, Eddington-inspired-Born-Infeld gravity and Ho$\check{\text{r}}$ava-Lifshitz gravity, the previous conclusion can also stand well in quantum cosmology induced from these modified gravities. This observation implies that there might be a universal relation between dark energy and normalizability of the cosmological wave function.
The solution of the field equations of the conformal theory of gravitation with Dirac scalar field in Cartan-Weyl spacetime at the very early Universe is obtained. In this theory dark energy (describing by an effective cosmological constant) is a function of the Dirac scalar field $β$. This solution describes the exponential decreasing of $β$ at the inflation stage and has a limit to a constant value of the dark energy at large time. This can give a way to solving the fundamental cosmological constant problem as a consequence of the fields dynamics in the early Universe.
We consider cosmological tests of a scalar-vector-tensor gravitational model, in which the dark energy is included in the total action through a gauge invariant, electromagnetic type contribution. The ground state of dark energy, corresponding to a constant potential $V$ is a Bose-Einstein type condensate with spontaneously broken U(1) symmetry. In another words dark energy appears as a massive vector field emerging from a superposition of a massless vector and a scalar field, the latter corresponding to the Goldstone boson. Two particular cosmological models, corresponding to pure electric an…
In this work, we investigate the dynamics of the interacting dark energy and dark matter in viable models of $f(R)$ gravity by using a standard framework of dynamical system analysis. A simple form of the interacting dark energy $Q=3αHρ_{m}$ is used to study three viable models of $f(R)$ gravity which are consistent with local gravity constraints and satisfying conditions for the cosmological viability. As a result, we find that the fixed points are slightly modified from those obtained in the standard non-interacting analysis of $f(R)$ gravity proposed so far in the literature. In our models …
The cosmological candidate fields for dark energy as quintessence, phantom and cosmological constant, are studied in terms of an entropic hypothesis imposed on the McVittie solution surrounded by dark energy. We certify this hypothesis as "$D$-bound-Bekenstein bound identification" for dilute systems and use it as a criterion to determine which candidate of dark energy can satisfy this criterion for a dilute McVittie solution. It turns out that only the cosmological constant can pass this criterion successfully while the quintessence and phantom fields fail, as non-viable dark energy fields fo…
We study pilgrim dark energy model by taking IR cut-offs as particle and event horizons as well as conformal age of the universe. We derive evolution equations for fractional energy density and equation of state parameters for pilgrim dark energy. The phantom cosmic evolution is established in these scenarios which is well supported by the cosmological parameters such as deceleration parameter, statefinder parameters and phase space of $ω_\vartheta$ and $ω'_\vartheta$. We conclude that the consistent value of parameter $μ$ is $μ<0$ in accordance with the current Planck and WMAP$9$ results.
The existence of interactions between dark matter and dark energy has been widely studied, since they can fit well the observational data and may provide new physics through such an interaction. In this work we analyze these models and investigate their potential relation with future cosmological singularities. We find that every future singularity found in the literature can be mapped into a singularity of the interaction term, that we call $Q$-singularity, where the energy flow between the dark components diverges. Furthermore, this framework allows to identify a new type of future singulari…
A proposal to study the original and new agegraphic dark energy in DGP braneworld cosmology is presented in this work. To verify our model with the observational data, the model is constrained by a variety of independent measurements such as Hubble parameter, cosmic microwave background anisotropies, and baryon acoustic oscillation peaks. The best fitting procedure shows the effectiveness of agegraphic parameter $n$ in distinguishing between the original and new agegraphic dark energy scenarios and subsequent cosmological findings. In particular, the result shows that in both scenarios, our un…
In this paper, a cosmological solution to Mimetic Dark Matter (MDM) for an exponential potential is provided. Then, a solution for the $0-i$ perturbed Einstein's differential equation of MDM is obtained based on an exponential potential that satisfies inflation for some initial conditions. Another general potential is suggested that incorporates inflation too. Then, quantum perturbations are included. The constants in the model can be tuned to be in agreement with the amplitude fluctuation of the cosmic microwave background (CMB) radiation. Finally, the spectral index is calculated for the sug…
A cosmological approach based on considering a cosmic background with non-zero torsion is shown in order to give an option of explaining a possible phantom evolution, not ruled out according to the current observational data. We revise some aspects of the formal schemes on torsion and, according them, we develop a formalism which can be an interesting alternative for exploring Cosmology.
It is well known that gravitons can convert into photons, and vice versa, in the presence of cosmological magnetic fields. We study this conversion process in the context of atomic dark matter scenario. In this scenario, we can expect cosmological dark magnetic fields, which are free from the stringent constraint from the cosmic microwave observations. We find that gravitons can effectively convert into dark photons in the presence of cosmological dark magnetic fields. The graviton-dark photon conversion effect may open up a new window for ultra high frequency gravitational waves.
We study spherically symmetric solutions with a scalar field in the shift-symmetric subclass of the Horndeski theory. Constructing an effective energy-momentum tensor of the scalar field based on the two-fluid model, we decompose the scalar field into two components: dark matter and dark energy.We find the dark-matter fluid is pressure-less, and its distribution of energy density obeys the inverse-square law. We show the scalar field dark matter can explain the galaxy rotation curve and discuss the time evolution of the dark matter in the cosmic background.
This brief contribution is devoted to phenomenological consequences of deviations from Lorentz invariance in gravity and dark matter. We will discuss main effects on cosmological observables and current constraints derived from astrophysical and cosmological data.
Dark energy is investigated from the perspective of quantum cosmology. It is found that, together with an appropriate normal ordering factor $q$, only when there is dark energy then can the cosmological wave function be normalized. This interesting observation may require further attention.
We study the main cosmological properties of the agegraphic dark energy model at the expansion and perturbation levels. Initially, using the latest cosmological data we implement a joint likelihood analysis in order to constrain the cosmological parameters. Then we test the performance of the agegraphic dark energy model at the perturbation level and we define its difference from the usual $Λ$CDM model. Within this context, we verify that the growth index of matter fluctuations depends on the choice of the considered agegraphic dark energy (homogeneous or clustered). In particular, assuming a …
The formalism of dark energy based on modeling speed of sound as a function of equation of state parameter is elaborated. A specific model which allows detailed study of cosmological constant boundary crossing is introduced and analytical solutions for the model dynamics are obtained. It is shown how in specific parameter regimes dark energy can be a transient phenomenon. It is further demonstrated how the model reproduces specific features of recent fits of dark energy $w(z)$ to observational data.
We investigate the dynamics of the generalized $Λ$CDM model, which the $Λ$ term is running with the cosmological time. The $Λ(t)$ term emerges from the covariant theory of the scalar field $ϕ$ with the self-interacting potential $V(ϕ)$. On the example of the model $Λ(t)=Λ_{\text{bare}}+\frac{α^2}{t^2}$ we show the existence of a mechanism of the modification of the scaling law for energy density of dark matter: $ρ_{\text{dm}}\propto a^{-3+λ(t)}$. We discuss the evolution of $Λ(t)$ term and pointed out that during the cosmic evolution there is a long phase in which this term is approximately co…
In this paper, we obtain a holographic model of dark energy using the fluid/gravity duality. This model will be dual to a higher dimensional Schwarzschild black hole, and we would use fluid/gravity duality to relate to the parameters of this black hole to such a cosmological model. We will also analyze the thermodynamics of such a solution, and discuss the stability model. Finally, we use cosmological data to constraint the parametric space of this dark energy model. Thus, we will use observational data to perform cosmography for this holographic model based on fluid/gravity duality.
Both scalar fields and (generalized) Chaplygin gases have been widely used separately to characterize the dark sector of the Universe. Here we investigate the cosmological background dynamics for a mixture of both these components and quantify the fractional abundances that are admitted by observational data from supernovae of type Ia and from the evolution of the Hubble rate. Moreover, we study how the growth rate of (baryonic) matter perturbations is affected by the dark-sector perturbations.
The original mimetic model was proposed to take the role of dark matter. In this paper we consider possible direct interactions of the mimetic dark matter with other matter in the universe, especially the standard model particles such as baryons and photons. By imposing shift symmetry, the mimetic dark matter field can only have derivative couplings. We discuss the possibilities of generating baryon number asymmetry and cosmic birefringence in the universe based on the derivative couplings of the mimetic dark matter to baryons and photons.
We consider scalar field models of dark energy interacting with dark matter through a coupling proportional to the contraction of the four-derivative of the scalar field with the four-velocity of the dark matter fluid. The coupling is realized at the Lagrangian level employing the formalism of Scalar-Fluid theories, which use a consistent Lagrangian approach for relativistic fluid to describe dark matter. This framework produces fully covariant field equations, from which we can derive unequivocal cosmological equations at both background and linear perturbations levels. The background evoluti…
We apply the holographic principle in the cosmological context through the nonadditive Tsallis entropy, used to describe the thermodynamic properties of nonstandard statistical systems such as the gravitational ones. Assuming the future event horizon as the infrared cutoff, we build a dark energy model free from cosmological inconsistencies, which includes standard thermodynamics and standard holographic dark energy as a limiting case. We thus describe the dynamics of Tsallis holographic dark energy in a flat FLRW background. Hence, we investigate cosmological perturbations in the linear regim…
Dark energy and light WIMP dark matter from the cosmological viewpoint
本文从重子、暗物质和暗能量密度对宇宙总物质-能量密度收支的贡献的天体物理数据中，给出了轻暗物质粒子和暗能量准粒子的质量估计。我们使用的量子宇宙学模型中，暗能量是一个凝聚的原始标量场的量子振荡。质量约为15 GeV的暗能量准粒子与7年WMAP和其他数据一致。准粒子可以通过破坏CP不变性衰变为重子、轻子和暗物质。WIMP的质量约为5 GeV，对应于重子和暗物质能量密度的观测值。这样的质量与CoGeNT、DAMA和CDMS的观测结果一致。暗能量的准粒子可以被记录为频率为~ 3.64 x 10^{24} 1/s的恒定辐射背景。暗物质粒子必须以信号的形式表现出来，其频率约为1.21 x 10^{24} 1/s，来自星系团的辐射，其中存在由暗物质产生的强烈引力场。
