共查询到20条相似文献，搜索用时 31 毫秒
1.
2.
Both dark energy and the thermodynamics on apparent horizon in cosmology have been broadly investigated in recent several
years. In order to maintain the continuity equation of the total matter in the universe, a new interacting dark energy in
the framework of Brans-Dicke theory is proposed. Considering this new interacting dark energy, an equilibrium thermodynamics
in Brans-Dicke theory is constructed successfully. Moreover, this new interacting dark energy can be regarded as arising from
the “Holographic Dark Energy” models. 相似文献
3.
The present work deals with universe bounded by the cosmological event horizon as a thermodynamical system which is irreversible in nature. Using non equilibrium thermodynamical approach the entropy variation on the event horizon has been evaluated. The additional term in the entropy variation depends on the irreversible process parameter. Finally, two dark energy models are presented and results are analyzed. 相似文献
4.
The interaction of modified holographic dark energy and dark matter with varying G in flat Kaluza Klein universe is considered. Further, we take infrared cutoff scale L as future event horizon. In this scenario, equations of state parameter as well as evolution are explored. We also check
the validity of the generalized second law of thermodynamics. It is interesting to mention here that our results show consistency
with the present observations. 相似文献
5.
In this work, we study universe bounded by apparent horizon as an irreversible thermodynamical system. Using the non equilibrium thermodynamical technique, the modified entropy variation on the apparent horizon has been evaluated in general. Two dark energy models are presented and results are analyzed. 相似文献
6.
Tanwi Bandyopadhyay 《Astrophysics and Space Science》2012,341(2):689-693
We discuss the generalized second law of thermodynamics in the braneworld scenario with induced gravity and curvature correction terms. To explain the present acceleration of the universe, a dark energy component has been chosen on the 3-brane in the form of Modified Chaplygin Gas together with a perfect fluid as the dark matter and we show that the GSLT is valid on the apparent horizon in late time. 相似文献
7.
We investigate the validity of the generalized second law of gravitational thermodynamics in a non-flat FRW universe containing
the interacting generalized Chaplygin gas with the baryonic matter. The boundary of the universe is assumed to be enclosed
by the dynamical apparent horizon. We show that for the interacting generalized Chaplygin gas as a unified candidate for dark
matter and dark energy, the equation of state parameter can cross the phantom divide. We also present that for the selected
model under thermal equilibrium with the Hawking radiation, the generalized second law is always satisfied throughout the
history of the universe for any spatial curvature, independently of the equation of state of the interacting generalized Chaplygin
gas model. 相似文献
8.
Here we consider our universe as homogeneous spherically symmetric FRW model and analyze the thermodynamics of this model
of the universe in scalar-tensor theory. Assuming the first law of thermodynamics validity of the generalized second law of
thermodynamics (GSLT) at the event horizon is examined in both the cases when the universe is filled with perfect fluid and
the holographic dark energy. 相似文献
9.
In this work, we have discussed the Maxwell’s electrodynamics in non-linear forms in FRW universe. The energy density and pressure for non-linear electrodynamics have been written in the electro-magnetic universe. The Einstein’s field equations for flat FRW model in loop quantum cosmology have been considered if the universe is filled with the matter and electro-magnetic field. We separately assumed the magnetic universe and electric universe. The interaction between matter and magnetic field have been considered in one section and for some particular form of interaction term, we have found the solutions of magnetic field and the energy density of matter. We have also considered the interaction between the matter and electric field and another form of interaction term has been chosen to solve the field equations. The validity of generalized second law of thermodynamics has been investigated on apparent and event horizons using Gibb’s law and the first law of thermodynamics for magnetic and electric universe separately. 相似文献
10.
G. F. R. Ellis W. R. Stoeger 《Monthly notices of the Royal Astronomical Society》2009,398(3):1527-1536
The causal limit usually considered in cosmology is the particle horizon, delimiting the possibilities of causal connection in the expanding Universe. However, it is not a realistic indicator of the effective local limits of important interactions in space–time. We consider here the matter horizon for the Solar system, i.e. the comoving region which has significantly contributed matter to our local physical environment. This lies inside the effective domain of dependence , which (assuming the universe is dominated by dark matter along with baryonic matter and vacuum-energy-like dark energy) consists of those regions that have had a significant active physical influence on this environment through effects such as matter accretion and acoustic waves. It is not determined by the velocity of light c , but by the flow of matter perturbations along their world lines and associated gravitational effects. We emphasize how small a region the perturbations which became our Galaxy occupied, relative to the observable universe – even relative to the smallest scale perturbations detectable in the cosmic microwave background radiation. Finally, looking to the future of our local cosmic domain, we suggest simple dynamical criteria for determining the present domain of influence and the future matter horizon . The former is the radial distance at which our local region is just now separating from the cosmic expansion. The latter represents the limits of growth of the matter horizon in the far future. 相似文献
11.
In this work, we have considered variable G in flat FRW universe filled with the mixture of dark energy, dark matter and radiation. If there is no interaction between
the three fluids, the deceleration parameter and statefinder parameters have been calculated in terms of dimensionless density
parameters which can be fixed by observational data. Also the interaction between three fluids has been analyzed due to constant
G. The statefinder parameters also calculated in two cases: pressure is constant and pressure is variable. 相似文献
12.
Ritabrata Biswas Nairwita Mazumder Subenoy Chakraborty 《Astrophysics and Space Science》2011,335(2):603-609
In this paper we deal with accretion of dark energy in the holographic dark energy model for a general non-rotating static
spherically symmetric black hole. The mass of the black hole increases or decreases depending on the nature of the holographic
dark energy (quintessence or phantom) as well as on some integration parameters. It is to be illustrated that the enhancement
or reduction of mass of a black hole is independent of the mass or size of the black hole itself. Rather it depends only upon
the radius of the event horizon of the universe. Finally, the generalized second law of thermodynamics has been studied on
the event horizon to be assured that the law holds even if when the black hole mass is decreasing though it is engrossing
some mass. 相似文献
13.
In this work we investigate the background dynamics when dark energy is coupled to dark matter with a suitable interaction
in the universe described by brane cosmology. Here DGP and the RSII brane models have been considered separately. Dark energy
in the form of modified Chaplygin gas is considered. A suitable interaction between dark energy and dark matter is considered
in order to at least alleviate (if not solve) the cosmic coincidence problem. The dynamical system of equations is solved
numerically and a stable scaling solution is obtained. A significant attempt towards the solution of the cosmic coincidence
problem is taken. The statefinder parameters are also calculated to classify the dark energy models. Graphs and phase diagrams
are drawn to study the variations of these parameters. It is also seen that the background dynamics of modified Chaplygin
gas is completely consistent with the notion of an accelerated expansion in the late universe. Finally, it has been shown
that the universe in both the models follows the power law form of expansion around the critical point, which is consistent
with the known results. 相似文献
14.
In this work, we consider the framework of non-linear electrodynamics in Bianchi type I universe model composed of matter and electromagnetic field. We deal with electric and magnetic universe separately. In this scenario, we calculate the electric and magnetic fields and their corresponding matter densities using two particular types of interaction terms. We also check the validity of generalized second law of thermodynamics in both universe models enclosed by apparent horizon. It turns out that this law holds on the apparent horizon for a particular range depending upon the parameters. Finally, we discuss the deceleration and statefinder parameters to check the viability of these models. 相似文献
15.
H. Farajollahi A. Ravanpak H. Shojaie M. Abolghasemi 《Astrophysics and Space Science》2014,350(1):325-331
This work is to study the generalized second law (GSL) of thermodynamics in tachyon cosmology where the tachyon field is coupled to the matter Lagrangian while the boundary of universe is assumed to be a dynamical apparent horizon. The two logarithmic and power law corrected entropy on the apparent horizon is also discussed and the conditions for validity of GSL in both scenarios are investigated by using observational data of Sne Ia. In comparison to other research works, since the model is constrained by observational data, the conditions obtained for the dimensionless constant parameter, α in both logarithmic and power law entropy correction of GSL are (physically) meaningful and realistic. The model also predicts an accelerating universe with no phantom crossing in the past or future. 相似文献
16.
This paper is aimed to investigate 5D holographic dark energy (HDE) in DGP-Brane cosmology by employing a combination of Sne Ia, BAO and CMB observational data and constraining cosmological parameters. The FRW dynamics for the normal branch (?=+1) solution of induced gravity brane-world model is taken with the assumption that matter in 5D bulk is HDE such that its holographic nature is reproduced effectively in 4D universe. In the HDE model, we used Hubble horizon as IR cutoff instead of future event horizon. This way, while the model predicts current universe acceleration, it also removes the problem of circular reasoning and causality observed in using future event horizon as IR cutoff. 相似文献
17.
The main goal of this work is investigation of NADE in the cyclic universe scenario. Since, cyclic universe is explained by
a phantom phase (ω<−1), it is shown when there is no interaction between matter and dark energy, ADE and NADE do not produce a phantom phase,
then can not describe cyclic universe. Therefore, we study interacting models of ADE and NADE in the modified Friedmann equation.
We find out that, in the high energy regime, which it is a necessary part of cyclic universe evolution, only NADE can describe
this phantom phase era for cyclic universe. Considering deceleration parameter tells us that the universe has a deceleration
phase after an acceleration phase, and NADE is able to produce a cyclic universe. Also it is found valuable to study generalized
second law of thermodynamics. Since the loop quantum correction is taken account in high energy regime, it may not be suitable
to use standard treatment of thermodynamics, so we turn our attention to the result of Li et al. (Adv. High Energy Phys. 2009:
905705, 2009), which the authors have studied thermodynamics in loop quantum gravity, and we show that which condition can satisfy generalized
second law of thermodynamics. 相似文献
18.
In this paper, the generalized second law (GSL) of thermodynamics and entropy is revisited in the context of cosmological
models with bouncing behavior such as chameleon cosmology where the boundary of the universe is assumed to be enclosed by
the dynamical apparent horizon. From a thermodynamic point of view, to link between thermodynamic and geometric parameters
in cosmological models, we introduce “entropy rate of change multiplied by the temperature” as a model independent thermodynamic
state parameter together with the well known {r,s} statefinder to differentiate the dark energy models. 相似文献
19.
Surajit Chattopadhyay 《Astrophysics and Space Science》2014,352(2):937-942
Considering power-law for of scale factor in a flat FRW universe we reported a reconstruction scheme for f(G) gravity based on QCD ghost dark energy. We reconstructed the effective equation of state parameter and observed “quintessence” behavior of the equation of state parameter. Furthermore, considering dynamical apparent horizon as the enveloping horizon of the universe we have observed that the generalized second law of thermodynamics is valid for this reconstructed f(G) gravity. 相似文献
20.
The most recently celebrated cosmological implications of the cosmic microwave background studies with WMAP (2006), though fascinating by themselves, do, however, create some extremely hard conceptual challenges for the present‐day cosmology. These recent extremely refined WMAP observations seem to reflect a universe which was extremely homogeneous at the recombination age and thus is obviously causally closed at the time of the cosmic recombination era. From the very tiny fluctuations apparent at this early epoch the presently observable nonlinear cosmic density structures can, however, only have grown up, if in addition to a mysteriously high percentage of dark matter an even higher percentage of dark energy is admitted as drivers of the cosmic evolution. The required dark energy density, on the other hand, is nevertheless 120 orders of magnitude smaller then the theoretically calculated value. These are outstanding problems of present day cosmology onto which we are looking here under new auspices. We shall investigate in the following, up to what degree a universe simply abolishes all these outstanding problems in case it reveals itself as an universe of constant total energy. As we shall show basic questions like: How could the gigantic mass of the universe of about 1080 proton masses at all become created? – Why is the presently recognized and obviously indispensable cosmic vacuum energy density so terribly much smaller than is expected from quantum theoretical considerations, but nevertheless terribly important for the cosmic evolution? – Why is the universe within its world horizon a causally closed system? –, can perhaps simply be answered, when the assumption is made that the universe has a constant total energy with the consequence that the total mass density of the universe (matter and vacuum) scales with . Such a scaling of matter and vacuum energy abolishes the horizon problem, and the cosmic vacuum energy density can easily be reconciled with its theoretical expectation values. In this model the mass of the universe increases linearly with the world extension Ru and can grow up from a Planck mass as a vacuum fluctuation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献