共查询到20条相似文献,搜索用时 15 毫秒
1.
Yousef Bisabr 《General Relativity and Gravitation》2009,41(2):305-313
We study the holographic dark energy model in a generalized scalar tensor theory. In a universe filled with cold dark matter
and dark energy, the effect of potential of the scalar field is investigated in the equation of state parameter. We show that
for a various types of potentials, the equation of state parameter is negative and transition from deceleration to acceleration
expansion of the universe is possible. 相似文献
2.
A. J. M. Medved 《General Relativity and Gravitation》2009,41(2):287-303
It has, quite recently, become fashionable to study a certain class of holographic-inspired models for the dark energy. These
investigations have, indeed, managed to make some significant advances towards explaining the empirical data. Nonetheless,
surprisingly little thought has been given to conceptual issues such as the composition and the very nature of the implicated
energy source. In the current discourse, we attempt to fill this gap by the way of some speculative yet logically self-consistent
arguments. Our construction takes us along a path that begins with an entanglement entropy and ends up at a Hubble-sized gas
of exotic particles. Moreover, our interpretation of the dark energy turns out to be suggestive of a natural resolution to
the cosmic-coincidence problem. 相似文献
3.
Sh. Khosravi E. Kourkchi R. Mansouri Y. Akrami 《General Relativity and Gravitation》2008,40(5):1047-1069
We present a new model universe based on the junction of FRW to flat Lemaitre–Tolman–Bondi (LTB) solutions of Einstein equations
along our past light cone, bringing structures within the FRW models. The model is assumed globally to be homogeneous, i.e.
the cosmological principle is valid. Local inhomogeneities within the past light cone are modeled as a flat LTB, whereas those
outside the light cone are assumed to be smoothed out and represented by a FRW model. The model is singularity free, always
FRW far from the observer along the past light cone, gives way to a different luminosity distance relation as for the CDM/FRW
models, a negative deceleration parameter near the observer, and correct linear and non-linear density contrast. As a whole,
the model behaves like a FRW model on the past light cone with a special behavior of the scale factor, Hubble and deceleration
parameter, mimicking dark energy.
Paper in honor of Bahram Mashhoon’s 60th birthday. 相似文献
4.
5.
We investigate thermal inflation in double-screen entropic cosmology. We find that its realization is general, resulting from the system evolution from non-equilibrium to equilibrium. Furthermore, going beyond the background evolution, we study the primordial curvature perturbations arising from the universe interior, as well as from the thermal fluctuations generated on the holographic screens. We show that the power spectrum is nearly scale-invariant with a red tilt, while the tensor-to-scalar ratio is in agreement with observations. Finally, we examine the non-Gaussianities of primordial curvature perturbations, and we find that a sizable value of the non-linearity parameter is possible due to holographic statistics on the outer screen. 相似文献
6.
Maik Stuke 《Progress in Particle and Nuclear Physics》2011,66(2):220-225
The total lepton asymmetry l=∑flf in our universe is only poorly constrained by theories and experiments. It might be orders of magnitudes larger than the observed baryon asymmetry b?O(10−10), |l|/b≤O(109). We found that the dynamics of the cosmic QCD transition changes for large asymmetries. Predictions for asymmetries in a single flavour lf allow even larger values. We find that asymmetries of lf≤O(1) in single or two flavours may change the relic abundance of WIMPs. However, large lepton and large individual lepton flavour asymmetries influence significantly the dynamics of the early universe between the electroweak phase transition and the onset of neutrino oscillations. 相似文献
7.
根据光致聚合物中光栅形成机制,应用数学模型与实验相结合的方法,研究了一种新型光致聚合物在全息记录中的暗增长现象.研究表明,应用不同写入光强使衍射效率达到相同的饱和程度后,前期的写入光较弱则对应后期的暗增长程度较强.为了利用暗增长过程提高衍射效率,设计并实施了非连续曝光实验,使曝光与暗增长过程交替进行.并且通过暗增长过程的实验数据拟合出该材料的扩散时间常量为21 s,据此设定非连续曝光的周期.结果表明,相同记录条件下,非连续曝光比连续曝光可以获得更高的衍射效率. 相似文献
8.
T. Padmanabhan 《General Relativity and Gravitation》2002,34(12):2029-2035
I provide a general proof of the conjecture that one can attribute an entropy to the area of any horizon. This is done by constructing a canonical ensemble of a subclass of spacetimes with a fixed value for the temperature T = –1 and evaluating the exact partition function Z(). For spherically symmetric spacetimes with a horizon at r = a, the partition function has the generic form Z exp[S – E], where S = (1/4)4 a
2 and |E| = (a/2). Both S and E are determined entirely by the properties of the metric near the horizon. This analysis reproduces the conventional result for the black-hole spacetimes and provides a simple and consistent interpretation of entropy and energy for De Sitter spacetime. For the Rindler spacetime the entropy per unit transverse area turns out to be (1/4) while the energy is zero. Further, I show that the relationship between entropy and area allows one to construct the action for the gravitational field on the bulk and thus the full theory. In this sense, gravity is intrinsically holographic. 相似文献
9.
We study the spontaneously induced general relativity (GR) from the scalar-tensor gravity. We demonstrate by numerical methods that a novel inner core can be connected to the Schwarzschild exterior with cosmological constants and any sectional curvature. Deriving an analytic core metric for a general exterior, we show that all the nontrivial features of the core, including the locally holographic entropy packing, are universal for the general exterior in static spacetimes. We also investigate whether the f(R) gravity can accommodate the nontrivial core. 相似文献
10.
Supermassive Black Holes are the most entropic objects found in the universe. The Holographic Bound (HB) to the entropy is used to constrain their formation time with initial masses 106–8
M
, as inferred from observations. We find that the entropy considerations are more limiting than causality for this direct formation. Later we analyze the possibility of SMBHs growing from seed black holes. The growth of the initial mass is studied in the case of accretion of pure radiation and quintessence fields, and we find that there is a class of models that may allow this metamorphosis. Our analysis generalizes recent work for some models of quintessence capable of producing a substantial growth in a short time, while simultaneously obeying the causal and Holographic Bound limits. 相似文献
11.
The holographic principle has revealed that phyical systems in 3-D space, black holes included, are basically two-dimensional as far as their information content is concerned. This conclusion is complemented by one sketched here: as far as entropy or information flow is concerned, a black hole behaves as a one-dimensional channel. We define a channel in flat spacetime in thermodynamic terms, and contrast it with common entropy emitting systems. A black hole is more like the former: its entropy output is related to the emitted power as it would be for a one-dimensional channel, and disposal of an information stream down a black hole is limited by the power invested in the same way as for a one-dimensional channel. 相似文献
12.
The dark enhancements with various exposure energies are studied in thick PQ/PMMA photopolymer. Considered the weak molecules diffusion of PQ component and the grating detuning, a new mechanism of dark reaction is proposed to explain the dark enhancement. Moreover, the influences of dark reaction on Bragg angular selectivity and grating recording are analyzed. The results are beneficial to the practical holography application. 相似文献
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14.
We consider the astrophysical and cosmological implications of the existence of a minimum density and mass due to the presence
of the cosmological constant. If there is a minimum length in nature, then there is an absolute minimum mass corresponding
to a hypothetical particle with radius of the order of the Planck length. On the other hand, quantum mechanical considerations
suggest a different minimum mass. These particles associated with the dark energy can be interpreted as the “quanta” of the
cosmological constant. We study the possibility that these particles can form stable stellar-type configurations through gravitational
condensation, and their Jeans and Chandrasekhar masses are estimated. From the requirement of the energetic stability of the
minimum density configuration on a macroscopic scale one obtains a mass of the order of 1055 g, of the same order of magnitude as the mass of the universe. This mass can also be interpreted as the Jeans mass of the
dark energy fluid. Furthermore we present a representation of the cosmological constant and of the total mass of the universe
in terms of ‘classical’ fundamental constants. 相似文献
15.
Ya Bo Wu Ming Hui Fu Fang Yuan Cheng Huan Huan Fu 《General Relativity and Gravitation》2009,41(8):1677-1693
In this paper a more general phenomenological model is proposed on the basis of the Hobbit model in Cardone et al. (Phys Rev
D 69:083517, 2004). The main purpose of constructing our model is to make this model can not only mimic the ΛCDM model, but
also describe a four-phase smooth transition of the universe, namely the inflationary phase, a radiation-dominated phase,
a matter-dominated phase and a de Sitter-like phase. In order to check whether this model is a viable one, the evolutions
of the universe are respectively discussed in the two cases, and the possible physical interpretations for this model are
also respectively shown by using the scalar fields. Finally, the structure formations in our model are simply discussed for
the both cases, and the results given by us reconfirm that our model can be regarded as a fit to the ΛCDM model, if we choose
the proper conditions. 相似文献
16.
Luis P. Chimento Mónica Forte Gilberto M. Kremer 《General Relativity and Gravitation》2009,41(5):1125-1137
A cosmological model for the present Universe is analyzed whose constituents are a non-interacting baryonic matter field and
interacting dark matter and dark energy fields. The dark energy and dark matter are coupled through their effective barotropic
indexes, which are considered as functions of the ratio of their energy densities. Two asymptotically stable cases are investigated
for the ratio of the dark energy densities which have their parameters adjusted by considering best fits to Hubble function
data. It is shown that the deceleration parameter, the density parameters, and the luminosity distance have the correct behavior
which is expected for a viable present scenario of the Universe. 相似文献
18.
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. 相似文献
19.
Manuel Barros José L. Cabrerizo Manuel Fernández 《General Relativity and Gravitation》2001,33(3):415-428
We obtain a reduction of the symmetry holographic principle for symmetric configurations of Nambu–Goto–Polyakov string theories in a semi-Riemannian space. The argument reduces the search of string configurations with a certain degree of symmetry to that for elastic curves in a corresponding orbit space. These solutions are solitons which are holographically related to particles that evolve along elastic worldlines in the orbit space. We also exhibit examples and applications to obtain soliton string shapes with cylindrical, rotational, toroidal etc. symmetry. In most of the cases we can determine the whole moduli space of symmetric solitons. 相似文献
20.
In the bottom-up approach to AdS/QCD based on a five-dimensional gravity dilaton action the exponential of the dilaton field is usually identified as the strong or 't Hooft coupling. There is currently no model known which fits the measurements of the running coupling and lattice results for pressure at the same time. With a one parametric toy model we demonstrate the effect of fitting the pressure on the coupling and vice versa. 相似文献