Quintessence anisotropic stellar models in quadratic and Born-Infeld modified teleparallel Rastall gravity

This study aims to discuss anisotropic solutions that are spherically symmetric in the quintessence field,which describe compact stellar objects in the modified Rastall teleparallel theory of gravity.To achieve this goal,the Krori and Barua arrangement for spherically symmetric components of the line element is incorporated.We explore the field equations by selecting appropriate off-diagonal tetrad fields.Born-Infeld function of torsion f(T)=β√λT+1-1 and power law form h(T)=δTn are used.The Born-Infeld gravity was the first modified teleparallel gravity to discuss inflation.We use the linear equation of state pr=ξρto separate the quintessence density.After obtaining the field equations,we investigate different physical parameters that demonstrate the stability and physical acceptability of the stellar models.We use observational data,such as the mass and radius of the compact star candidates PSRJ 1416-2230,Cen X-3,&4U 1820-30,to ensure the physical plausibility of our findings.

Constraints on Asymmetric Dark Matter in Quintessence Model

The modified cosmology like quintessence model with kination phase predicted the Hubble expansion rate of the universe before Big Bang Nucleosynthesis is different from the standard cosmological scenario. The modified expansion rate leaves its imprint on the relic density of asymmetric dark matter. In this work, we review the calculation of relic density of asymmetric WIMP dark matter in the standard cosmological scenario and quintessence model with kination phase. Then we use the Planck data to find constraints on the annihilation cross section and the mass of the asymmetric dark matter in those models.

The Reissner-Nordström black hole surrounded by quintessence may not be destroyed

In the study of weak cosmic censorship conjectures(WCCC),some research finds that the Reissner-Nordström black hole might be destroyed by a test particle with particular mass and charge under some conditions,which means that the naked singularity of the black hole could be observed.This is not allowed in WCCC.We have never observed such naked singularities which should not exist in theory,so we need to find a proper way to protect the black hole from being destroyed by such particles.In this paper,we study a Reissner-Nordström black hole that is surrounded by quintessence(RN-Q)and find that the black hole would be stable and safe because of the effective potential barrier induced by the quintessence term.This result may also show in a sense that the quintessence might have more potential value.

Quintessence黑洞的视界面积量子化

近年来的天文观测发现了暗能量的存在,因而有必要讨论暗能量条件下的黑洞热力学。该文应用约化相空间量子化方法研究了被Quintessence包围的静态球对称黑洞的视界面积量子化问题,给出了面积谱。

Quintessence包围下黑洞的爱因斯坦引力场方程

本文首先阐述近年来有关黑洞的爱因斯坦引力场方程的研究概况及其意义。其次,介绍了静态球对称黑洞在计算其爱因斯坦引力场方程的理论基础和计算方法。文章最后,展示计算Quintessence包围下黑洞的爱因斯坦引力场方程得出的结果,并对结果进行讨论分析。

Quasi-Local Energy Distribution and Thermodynamics of Reissner-Nordstrom Black Hole Surrounded by Quintessence

We investigate quasi-local energy distribution and thermodynamics of the Reissner-Nordstr6m black hole space-time surrounded by quintessence. We use the quasi-local energy distribution from Einstein energy-momentum complex. We plot the variation of the energies, temperature and heat capacity with the state parameter related to the quintessence ωq. We show that due to the presence of quintessence, the total energy of the outer region as well as the temperature and heat capacity decreases with the increase of the density of quintessence, while the total energy of the black hole region increases.

Tunneling Radiation from a Static Spherically Symmetric Black Hole Surrounded by Quintessence

By extending the Parikh-Wilczek tunneling framework,we investigate the tunneling radiation of unchargedmassless particles from a static spherically symmetric black hole surrounded by quintessence.The results are consistentwith an underlying unitary theory.

隧穿方法和quintessence物质环绕Reissner-Nrdstrom黑洞的修正熵

利用隧穿方法,给出了有quintessence物质环绕的Reissner-Nrdstrom黑洞经典霍金温度的量子修正,进而利用热力学第二定律计算了经典Bekenstein-Hawking熵及其量子修正,所得结果主要由经典黑洞熵及其对数修正项和非对数修正项三部分组成.

Is Quintessence an Indication of a Time-Varying Gravitational Constant?

A model is presented where the quintessence parameter, w, is related to a time-varying gravitational constant. Assuming a present value of w = -0.98 , we predict a current variation of ?/G = -0.06H0, a value within current observational bounds. H0 is Hubble’s parameter, G is Newton’s constant and ? is the derivative of G with respect to time. Thus, G has a cosmic origin, is decreasing with respect to cosmological time, and is proportional to H0, as originally proposed by the Dirac-Jordan hypothesis, albeit at a much slower rate. Within our model, we can explain the cosmological constant fine-tuning problem, the discrepancy between the present very weak value of the cosmological constant, and the much greater vacuum energy found in earlier epochs (we assume a connection exists). To formalize and solidify our model, we give two distinct parametrizations of G with respect to “a”, the cosmic scale parameter. We treat G-1 as an order parameter, which vanishes at high energies;at low temperatures, it reaches a saturation value, a value we are close to today. Our first parametrization for G-1 is motivated by a charging capacitor;the second treats G-1(a) by analogy to a magnetic response, i.e., as a Langevin function. Both parametrizations, even though very distinct, give a remarkably similar tracking behavior for w(a) , but not of the conventional form, w(a) = w0 + wa(1-a) , which can be thought of as only holding over a limited range in “a”. Interestingly, both parametrizations indicate the onset of G formation at a temperature of approximately 7×1021 degrees Kelvin, in contrast to the ΛCDM model where G is taken as a constant all the way back to the Planck temperature, 1.42×1032 degrees Kelvin. At the temperature of formation, we find that G has increased to roughly 4×1020 times its current value. For most of cosmic evolution, however, our variable G model gives results similar to the predictions of the ΛCDM model, except in the very early universe, as we shall demonstrate. In fact, in the limit where w approaches -1, the expression, ?/G , vanishes, and we are left with the concordance model. Within our framework, the emergence of dark energy over matter at a scale of a ≈ 0.5 is that point where G-1 increases noticeably to its current value, G0-1 . This weakening of G to its current value G0 is speculated as the true cause for the observed unanticipated acceleration of the universe.

Kinetical Inflation and Quintessence by F-Harmonic Map

We were interested, along this work, in the phenomena of the quintessence and the inflation due to the F-harmonic maps, in other words, in the functions of the scalar field such as the exponential and trigo-harmonic maps. We showed that some F-harmonic map such as the trigonometric functions instead of the scalar field in the lagrangian, allow, in the absence of term of potential, reproduce the inflation. However, there are other F-harmonic maps such as exponential maps which can’t produce the inflation;the pressure and the density of this exponential harmonic field being both of the same sign. On the other hand, these exponential harmonic fields redraw well the phenomenon of the quintessence when the variation of these fields remains weak. The problem of coincidence, however remains.

Quintessence黑洞的量子隧穿效应以及黑洞遗迹

天文观测发现了暗能量的存在,因此可以讨论暗能量所包围的静态球对称黑洞。运用了Parikh的量子隧穿模型,研究了Quintessence黑洞的量子隧穿过程以及黑洞遗迹问题。结果表明,在能量守恒的条件下,黑洞外视界和宇宙视界处的粒子出射率与Bekenstein-Hawking熵有关,辐射谱不再是严格的纯热谱。在考虑一级修正后得到具有对数项的粒子隧穿几率,并讨论了黑洞遗迹的存在的可能性。

Quintessence物质包围的整体单极子黑洞的熵

本文利用薄膜模型方法计算Quintessence物质包围的整体单极子黑洞的熵。薄膜模型的应用克服了原始砖墙模型中的小质量近似和对数项忽略等不自然的操作。计算结果表明,该黑洞的熵是黑洞视界面积和宇宙视界面积之和的1/4倍,完全符合贝肯斯坦-霍金熵的面积公式。

Charged Randall-Sundrum Braneworld Type Ⅱ with Higher Order Curvature Corrections from Superstring Arguments and Dominated by Quintessence

We discuss a new class of RSII braneworld cosmology exhibiting accelerated expansion and dominated by quintessence. It is explicitly demonstrated that the universe expansion history （transition from inflation to deceleration epoch to acceleration and effective quintessence era） may naturally occur in such unified theory for some classes of inverse scalar potentials. Besides a decaying effective cosmological constant, the model incorporates an increasing black hole mass, an increasing Maxwellian electrical charge with cosmic time and a time-dependent brahe tension. The cosmological model exhibits several features of cosmological and astrophysical interest for both the early and late universe consistent with recent observations, in particular the ones concerned with the gravitational constants, black holes masses and charges and variation of the gauge coupling parameters with cosmic time. One interesting mark of the constructed model concerns the fact that a black hole mass surrounded by quintessence energy may increase with time even if the horizon disappears.

Some characteristics of three exact solutions of Einstein equations minimally coupled to a Quintessence field

We show some characteristics of three exact solutions to Einstein＇s gravity equation minimally coupled to a Quintessence field. Besides eternal inflation, several other interesting inflationary processes, such as transitory inflation, are obtained in these solutions. Singularity is avoided in some special cases.

Dirac Quasinormal Modes of Reissner-Ndstrom Black Hole Surrounded by Quintessence

Using the third-order WKB approximation, we evaluate the quasinormal frequencies of massless Dirac field perturbation around a Reissner Nordstrom black hole surrounded by a static and spherically symmetric quintessence. We study the variation of quasinormal frequencies with the quintessential state parameter ε, the total angular momentum number ｜k｜, the charge Q, and the overtone number n changes, respectively. Moreover, from the results we obtained, we find that the massless Dirac field damps more slowly due to the presence of quintessence.

Gravitational frequency-shift and deflection of light by quintessence

In this paper we investigate the gravitational frequency-shift and deflection of light in the Schwarzschild black hole space-time surrounded by quintessence. With the analytical and numerical methods, we find that the gravitational frequency-shift of light in the Schwarzschild black hole space-time surrounded by the quintessence increases as the values of the normalization factor c increases, but the gravitational frequency-shift of light decreases with the quintessential state parameter Wq increasing. We also calculate the deflection of light by quintessence and find that the deflection rate decreases as the values of the quintessential parameters c and Wq increase.

Approximate w_φ～Ω_φ Relations in Quintessence Models

Quintessence field is a widely-studied candidate of dark energy. There is ＂tracker solution＂ in quintessence models, in which evolution of the field φ at present times is not sensitive to its initial conditions. When the energy density of dark energy is negleetable （Ωφ 〈〈 1）, evolution of the tracker solution can be well analysed from ＂tracker equation＂. In this paper, we try to study evolution of the quintessence field from ＂full tracker equation＂, which is valid for all spans of Ωφ. We get stable fixed points of we and wφ （noted as wφ and Ωφ） from the ＂full tracker equation＂, i.e., we and ωφ will always approach ωφ and Ωφ respectively. Since wφ and Ωφ are analytic functions of φ, analytic relation of φ can be obtained, which is a good approximation for the we φ relation and can be obtained for the most type of quintessence potentials. By using this approximation, we find that inequalities ωφ 〈 we and 〈ωφ are statisfied if the we （or ωφ） decreases with time. In this way, the potentiai U（φ） can be constrained directly from observations, by no need of solving the equations of motion numerically.

Statefinder Parameters for Coupled Quintessence Scenario in a Power Law Case

We investigate a coupled quintessence scenario, which can provide a natural solution to the cosmic coincidence problem. We assume that the mass of dark matter particles depends on a power law function of the scalar field associated to dark energy and meanwhile the scalar field evolves in a power law potential. Since the dynamics of this system is dominated by an attractor solution, the mass of dark matter particles is forced to change with time as to ensure that the ratio between the energy densities of dark matter and dark energy becomes a constant at late times,and one thus solves the cosmic coincidence problem naturally. We then apply a statefinder diagnostic to this coupled quintessence scenario. It is shown that the evolving trajectory of this scenario in the s-r diagram is quite different from those of other dark energy models.

Quantum Non-thermal Effect from Black Holes Surrounded by Quintessence

We present a short and direct derivation of Hawking radiation as a tunneling process across the horizonand compute the tunneling probability.Considering the self-gravitation and energy conservation,we use the Keski-Vakkuri,Kraus,and Wilczek(KKW)analysis to compute the temperature and entropy of the black holes surrounded byquintessence and obtain the temperature and entropy are different from the Hawking temperature and the Bekenstein-Hawkingentropy.The result we get can offer a possible mechanism to deal with the information loss paradox becausethe spectrum is not purely thermal.

Thermodynamic properties of Reissner-Nordstrm-de Sitter quintessence black holes

The mass,electric charge,and temperature of black holes in the Reissner-Nordstrm-de Sitter quintessence（RN-dSQ） spacetime are obtained.The heat capacities of the RN-dSQ black holes for certain electric charges and masses are analyzed.The electrostatic energy and dark energy in the RN-dSQ black holes are also calculated.