Time-like geodesic structure of a spherically symmetric black hole in the brane-world

Recently Malihe Heydari-Fard obtained a spherically symmetric exterior black hole solution in the brane-world scenario, which can be used to explain the galaxy rotation curves without postulating dark matter. By analysing the particle effective potential, we have investigated the time-like geodesic structure of the spherically symmetric black hole in the brane-world. We mainly take account of how the cosmological constant α and the stellar pressure β affect the time-like geodesic structure of the black hole. We find that the radial particle falls to the singularity from a finite distance or plunges into the singularity, depending on its initial conditions. But the non-radial time-like geodesic structure is more complex than the radial case. We find that the particle moves on the bound orbit or stable (unstable) circle orbit or plunges into the singularity, or reflects to infinity, depending on its energy and initial conditions. By comparing the particle effective potential curves for different values of the stellar pressure β and the cosmological constant α, we find that the stellar pressure parameter β does not affect the time-like geodesic structure of the black hole, but the cosmological constant α has an impact on its time-like geodesic structure.     

Reconstructing dark energy potentials from parameterized deceleration parameters

In this paper, the properties of dark energy are investigated according to the parameterized deceleration parameter q(z), which is used to describe the extent of the accelerating expansion of the universe. The potential of dark energy V(φ) and the cosmological parameters, such as the dimensionless energy density \varOmega_φ, \varOmega_m, and the state parameter w_φ, are connected to it. Concretely, by giving two kinds of parameterized deceleration parameters q(z)=a+bz/(1+z) and q(z)=1/2+(az+b)/(1+z)^2, the evolution of these parameters and the reconstructed potentials V(φ) are plotted and analysed. It is found that the potentials run away with the evolution of universe.     

Quadratic interaction effect on the dark energy density in the universe

In this study, we deal with the holographic model of interacting dark components of dark energy and dark matter quadratic case of the equation of state parameter(Eo S). The effective equations of states for the interacting holographic energy density are derived and the results are analyzed and compared with the solution of the linear form in the literature.The result of our work shows that the value of interaction term between dark components affects the fixed points at far future in the DE-dominated universe in the case of quadratic Eo S parameter; it is a different result from the linear case in the theoretical results in the literature, and as the Quintom scenario the equations of state had coincidence at the cosmological constant boundary of -1 from above to below.     

Constraints on the unified model of dark matter and dark energy

Using recently observed data:the Constitution dataset of type supernovae Ia (SNIa),the observational Hubble data (OHD),the measurement results of baryon acoustic oscillation (BAO) from the Sloan Digital Sky Survey (SDSS) and the Two Degree Field Galaxy Redshift Survey (2dFGRS),and the current cosmic microwave background (CMB) data from the five-year Wilkinson Microwave Anisotropy Probe (WMAP),we apply the Markov Chain Monte Carlo method to investigate the observational constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy.For this unified model,the constraints on GCG mixture are discussed by considering the different expressions of current matter density or considering constraints as being independent of the matter quantity Ωm.     

Effects of dark energy interacting with massive neutrinos and dark matter on universe evolution

In this paper we investigate the evolution of the cosmology model with dark energy interacting with massive neutrinos and dark matter. Using the numerical method to investigate the dynamical system, we find that the stronger the interaction between dark energy and dark matter, the lower the ratio of dark matter in the universe is; also, the stronger the interaction between dark energy and massive neutrinos, the lower the ratio of massive neutrinos in the universe is. On the other hand, the interaction between dark energy and dark matter or massive neutrinos has an effect on disturbing the universe's acceleration; we also find that our universe is still accelerating.     

Multi-pole dark energy

A scalar field with a pole in its kinetic term is often used to study cosmological inflation; it can also play the role of dark energy, which is called the pole dark energy model. We propose a generalized model where the scalar field may have two or even multiple poles in the kinetic term, and we call it the multi-pole dark energy. We find that the poles can place some restrictions on the values of the original scalar field with a non-canonical kinetic term. After the transformation to the canonical form, we get a flat potential for the transformed scalar field even if the original field has a steep one. The late-time evolution of the universe is obtained explicitly for the two pole model, while dynamical analysis is performed for the multiple pole model. We find that it does have a stable attractor solution, which corresponds to the universe dominated by the potential of the scalar field.     

第三讲宇宙中的暗物质和暗能量

文章对暗物质粒子的候选者和宇宙中暗能量的研究现状作一简单介绍．     

第三讲 宇宙中的暗物质和暗能量

文章对暗物质粒子的候选者和宇宙中暗能量的研究现状作一简单介绍.     

Entanglement in holographic dark energy models

We study a process of equilibration of holographic dark energy (HDE) with the cosmic horizon around the dark-energy dominated epoch. This process is characterized by a huge amount of information conveyed across the horizon, filling thereby a large gap in entropy between the system on the brink of experiencing a sudden collapse to a black hole and the black hole itself. At the same time, even in the absence of interaction between dark matter and dark energy, such a process marks a strong jump in the entanglement entropy, measuring the quantum-mechanical correlations between the horizon and its interior. Although the effective quantum field theory (QFT) with a peculiar relationship between the UV and IR cutoffs, a framework underlying all HDE models, may formally account for such a huge shift in the number of distinct quantum states, we show that the scope of such a framework becomes tremendously restricted, devoid virtually any application in other cosmological epochs or particle-physics phenomena. The problem of negative entropies for the non-phantom stuff is also discussed.     

粒子物理和宇宙学中的两片乌云——谈暗物质和暗能量

宇宙暗物质和暗能量是21世纪粒子物理和宇宙学研究中的两个重大的科学问题.文章首先简述了宇宙学研究的历史和现状以及对粒子物理学提出的新的挑战,接着较详细地介绍了暗物质、暗能量和反物质相关的科学问题以及在国际上这个研究领域近年来所取得的进展,最后展望了中国在暗物质和暗能量实验探测研究方面的前景.     

Detecting dark energy in long baseline neutrino oscillations

In this paper, we discuss a possibility of studying properties of dark energy in long baseline neutrino oscillation experiments. We consider two types of models of neutrino dark energy. For one type of models the scalar field is taken to be quintessence-like and for the other phantom-like. In these models the scalar fields couple to the neutrinos to give rise to spatially varying neutrino masses. We will show that the two types of models predict different behaviors of the spatial variation of the neutrino masses inside the Earth and consequently result in different signals in long baseline neutrino oscillation experiments.     

Revisiting the interacting model of new agegraphic dark energy

In this paper,a new version of the interacting model of new agegraphic dark energy(INADE)is proposed and analyzed in detail.The interaction between dark energy and dark matter is reconsidered.The interaction term Q=bH0ραdeρ1αdm is adopted,which abandons the Hubble expansion rate H and involves bothρde andρdm.Moreover,the new initial condition for the agegraphic dark energy is used,which solves the problem of accommodating baryon matter and radiation in the model.The solution of the model can be given using an iterative algorithm.A concrete example for the calculation of the model is given.Furthermore,the model is constrained by using the combined Planck data(Planck+BAO+SNIa+H0)and the combined WMAP-9 data(WMAP+BAO+SNIa+H0).Three typical cases are considered:(A)Q=bH0ρde,(B)Q=bH0√ρdeρdm,and(C)Q=bH0ρdm,which correspond toα=1,1/2,and 0,respectively.The departures of the models from theΛCDM model are measured by the BIC and AIC values.It is shown that the INADE model is better than the NADE model in the fit,and the INADE(A)model is the best in fitting data among the three cases.     

Dynamical interactions of dark energy and dark matter:Yang-Mills condensate and QCD axions

We analyze a model of cold axion dark matter weakly coupled with a dark gluon condensate,reproducing dark energy.We first review how to recover the dark energy behavior using the functional renormalization group approach,and ground our study in the properties of the effective Lagrangian,to be determined non-perturbatively.Then,within the context of G_(SM)×SU(2)_D×U(1)_(P Q),we consider Yang-Mills condensate(YMC)interactions with QCD axions.We predict a transfer of dark energy density into dark matter density,that can be tested in the next generation of experiments dedicated to dark energy measurements.We obtain new bounds on the interactions between the Yang-Mills condensate and axion dark matter from Planck data:the new physics interaction scale related to the axion/gluon condensate mixing is constrained to be higher than the 10~6GeV energy scale.     

粒子物理和宇宙学中的两片乌云——谈暗物质和暗能量

宇宙暗物质和暗能量是21世纪粒子物理和宇宙学研究中的两个重大的科学问题.文章首先简述了宇宙学研究的历史和现状以及对粒子物理学提出的新的挑战,接着较详细地介绍了暗物质、暗能量和反物质相关的科学问题以及在国际上这个研究领域近年来所取得的进展,最后展望了中国在暗物质和暗能量实验探测研究方面的前景.     

Effect of dark energy models on the energy content of charged and rotating black holes

The energy content of the charged-Kerr(CK)spacetime surrounded by dark energy(DE)is investigated using approximate Lie symmetry methods for the differential equations.For this,we consider three different DE scenarios:cosmological constant with an equation of state parameter$ω_q=-2/3,quintessence DE with an equation of state parameterω_c=-1,and a frustrated network of cosmic strings with an equation of state parameterω_n=-1/3.To study the gravitational energy of the CK black hole surrounded by the DE,we explore the symmetries of the 2nd-order perturbed geodesic equations.It is noticed,for all the values ofω,the exact symmetries are recovered as 2nd-order approximate trivial symmetries.These trivial approximate symmetries give the rescaling of arc length parameter s in this spacetime which indicates that the energy in the underlying spacetime has to be rescaled by a factor that depends on the black hole parameters and the DE parameter.This rescaling factor is compared with the factor of the CK spacetime found in[Hussain et al.Gen.Relativ.Gravit.(2009)]and the effects of the DE on it are discussed.It is observed that for all the three values of the equation of state parameterω,the effect of DE results in decreased energy content of the black hole spacetime,regardless of values of the charge Q,spin a and the DE parameterα.This reduction in the energy content due to the involvement of the DE favours the idea of mass reduction of black holes by accretion of DE given by[Babichev et al.Phys.Rev.Lett.(2004)].     

Using atom interferometry to detect dark energy

We review the tantalising prospect that the first evidence for the dark energy driving the observed acceleration of the universe on giga-parsec scales may be found through metre scale laboratory-based atom interferometry experiments. To do that, we first introduce the idea that scalar fields could be responsible for dark energy and show that in order to be compatible with fifth force constraints, these fields must have a screening mechanism which hides their effects from us within the solar system. Particular emphasis is placed on one such screening mechanism known as the chameleon effect where the field’s mass becomes dependent on the environment. The way the field behaves in the presence of a spherical source is determined and we then go on to show how in the presence of the kind of high vacuum associated with atom interferometry experiments, and when the test particle is an atom, it is possible to use the associated interference pattern to place constraints on the acceleration due to the fifth force of the chameleon field – this has already been used to rule out large regions of the chameleon parameter space and maybe one day will be able to detect the force due to the dark energy field in the laboratory.     

Holographic dark energy from acceleration of particle horizon

Following the holographic principle, which suggests that the energy density of dark energy may be inversely proportional to the area of the event horizon of the Universe, we propose a new energy density of dark energy through the acceleration of the particle horizon scaled by the length of this parameter. The proposed model depends only on one free parameter: begin{document}$ beta approx 0-1.99 $end{document}. For values of begin{document}$ beta $end{document} near zero, the deviation between the proposed model and the begin{document}$ mathrm{Lambda } $end{document} CDM model is significant, while for begin{document}$ beta to 1.99 $end{document}, the suggested model has no conflict with the begin{document}$ mathrm{Lambda } $end{document} CDM theory. Regardless of the value of begin{document}$ beta $end{document}, the model considers dark energy to behave as matter with positive pressure in high redshifts, begin{document}$ {omega }_{X}approx 0.33 $end{document}, while for present and near-future Universe, it is considered to behave similar to that in the cosmological constant model and phantom field. Comparing the model with the Ricci dark energy model, we show that our model reduces the errors of the Ricci dark energy model concerning the calculation of the age of old supernovae and evolution of different cosmic components in high redshifts. Moreover, we calculated matter structure formation parameters such as the CMB temperature and matter power spectrum of the model to consider the effects of matter-like dark energy during the matter-dominated era.     

Cosmic age problem revisited in the holographic dark energy model

Because of an old quasar APM 08279+5255$08279+5255$ at z=3.91$z=3.91$, some dark energy models face the challenge of the cosmic age problem. It has been shown by Wei and Zhang [H. Wei, S.N. Zhang, Phys. Rev. D 76 (2007) 063003, arXiv:0707.2129 [astro-ph]] that the holographic dark energy model is also troubled with such a cosmic age problem. In order to accommodate this old quasar and solve the age problem, we propose in this Letter to consider the interacting holographic dark energy in a non-flat universe. We show that the cosmic age problem can be eliminated when the interaction and spatial curvature are both involved in the holographic dark energy model.     

de Sitter spacetime: effects of metric perturbations on geodesic motion

Gravitational perturbations of the de Sitter spacetime are investigated using the Regge–Wheeler formalism. The set of perturbation equations is reduced to a single second order differential equation of the Heun-type for both electric and magnetic multipoles. The solution so obtained is used to study the deviation from an initially radial geodesic due to the perturbation. The spectral properties of the perturbed metric are also analyzed. Finally, gauge- and tetrad-invariant first-order massless perturbations of any spin are explored following the approach of Teukolsky. The existence of closed-form, i.e. Liouvillian, solutions to the radial part of the Teukolsky master equation is discussed.