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401.
Michael?Heller Leszek?Pysiak Wies?aw?Sasin Zdzis?aw?Golda 《General Relativity and Gravitation》2009,41(7):1625-1637
Heller et al. (J Math Phys 46:122501, 2005; Int J Theor Phys 46:2494, 2007) proposed a model unifying general relativity and
quantum mechanics based on a noncommutative algebra defined on a groupoid having the frame bundle over space–time as its base space. The generalized Einstein equation is assumed
in the form of the eigenvalue equation of the Einstein operator on a module of derivations of the algebra . No matter sources are assumed. The closed Friedman world model, when computed in this formalism, exhibits two interesting
properties. First, generalized eigenvalues of the Einstein operator reproduce components of the perfect fluid energy-momentum
tensor for the usual Friedman model together with the corresponding equation of state. One could say that, in this case, matter
is produced out of pure (noncommutative) geometry. Second, owing to probabilistic properties of the model, in the noncommutative
regime (on the Planck level) singularities are irrelevant. They emerge in the process of transition to the usual space–time
geometry. These results are briefly discussed. 相似文献
402.
G. S. Khadekar Vaishali Kamdi Cenap Ozel 《International Journal of Theoretical Physics》2009,48(2):373-379
In this paper we investigate the Λ-CDM universe by selecting the specific time dependent form of Λ, viz.
, in the context of 5-dimensional space time. Time-dependent form of equation of state parameter w is derived along with a possible signature flip of deceleration parameter q. It is also observed that a present age of the Universe, calculated for some specific values of parameter agrees very well
with the observational data. 相似文献
403.
Mauricio Bellini 《General Relativity and Gravitation》2001,33(11):2081-2091
I consider the COBE data coarse–grained field that characterize the now observable universe for a model of warm inflation which takes into account the thermally coupled fluctuations of the scalar field with the thermal bath. The power spectrum for both, matter and metric fluctuations are analyzed. I find that the amplitude for the fluctuations of the metric during the horizon entry should be very small for the expected values of temperature. 相似文献
404.
WUNing GermanoResconi ZHENGZhi-Peng XUZhan ZHANGDa-Hua RIJANTu-Nan 《理论物理通讯》2003,40(2):253-256
Based on geometry picture of gravitational gauge theory, the cosmological constant is determined theoreti-cally. The cosmological constant is related to the average energy density of gravitational gauge field. Because the energy density of gravltatlona] gauge field is negative, the cosmological constant is positive, which generates repulasive force on stars to make the expansion rate of the Universe accelerated. A rough estimation of it gives out its magnitude of the order of about 10^52m^-2, which is well consistent with experimental results. 相似文献
405.
Recently the background independent nonperturbative quantization has been extended to various theories of gravity and the corresponding quantum effective cosmology has been derived, which provides us with necessary avenue to explore the pre-inflationary dynamics. Brans-Dicke (BD) loop quantum cosmology (LQC) is one of such theories whose effective background dynamics is considered in this article. Starting with a quantum bounce, we explore the pre-inflationary dynamics of a universe sourced by a scalar field with the Starobinsky potential in BD-LQC. Our study is based on the idea that though Einstein's and Jordan's frames are classically equivalent up to a conformal transformation in BD theory, this is no longer true after quantization. Taking the Jordan frame as the physical one we explore in detail the bouncing scenario which is followed by a phase of a slow roll inflation. The three phases of the evolution of the universe, namely, bouncing, transition from quantum bounce to classical universe, and the slow roll inflation, are noted for an initially kinetic energy dominated bounce. In addition, to be consistent with observations, we also identify the allowed phase space of initial conditions that would produce at least 60 e-folds of expansion during the slow roll inflation. 相似文献
406.
We consider a holographic extended phase space in the presence of Reissner-Nordstrom-Anti-de Sitter(RNAdS) and Born-Infeld-Anti-de Sitter(BI-AdS) black holes in the bulk. In this extended phase space the cosmological constant is investigated as pressure and volume is defined as the codimension one-time slice in the bulk geometry enclosed by the minimal area appearing in the computation of the holographic entanglement entropy. These thermodynamics quantities can serve as probes of the underlying phase transition dictated by black hole thermodynamics, but do not describe different structures. We find that the isocharges on the pressure-volume plane exhibit a Van der Waals-like structure, for RN-AdS black holes in the background. For BI-AdS black holes, we observe the analogy with a Van der Waals liquid-gas system for βQ 1/2 and Reentrant phase transition for βQ 1/2 in the holographic extended phase space. The same holographic thermodynamic behavior is observed when we use the fidelity susceptibility as the volume and the cosmological constant as the pressure for RN-AdS black hole in the background. 相似文献
407.
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. 相似文献
408.
Method of determining cosmological parameter ranges with samples of candles with an intrinsic distribution 下载免费PDF全文
In this paper, the effect of the intrinsic distribution of cosmological candles is
investigated. We find that in the case of a narrow distribution the deviation of the
observed modulus of sources from the expected central value can be estimated within
a ceratin range. We thus introduce lower and upper limits of X2, X
min2 and Xmax2 to estimate cosmological parameters by
applying the conventional minimizing X2 method. We apply this method to a
gamma-ray burst (GRB) sample as well as to a combined sample including this GRB
sample and an SN Ia sample. Our analysis shows that: a) in the case of assuming an
intrinsic distribution of candles of the GRB sample, the effect of the distribution
is obvious and should not be neglected; b) taking into account this effect would
lead to a poorer constraint of the cosmological parameter ranges. The analysis
suggests that in the attempt of constraining the cosmological model with current GRB
samples, the results tend to be worse than was previously anticipated if the
mentioned intrinsic distribution does exist. 相似文献
409.
In order to relate the probabilistic predictions of quantum theory uniquely to measurement results, one has to conceive of an ensemble of identically prepared copies of the quantum system under study. Since the universe is the total domain of physical experience, it cannot be copied, not even in a thought experiment. Therefore, a quantum state of the whole universe can never be made accessible to empirical test. Hence the existence of such a state is only a metaphysical idea. Despite prominent claims to the contrary, recent developments in the quantum-interpretation debate do not invalidate this conclusion. 相似文献
410.
The Einstein's general relativity is formulated in the Hamiltonian form for a spatially flat, isotropic and homogeneous universe. Subsequently, we perform the canonical quantization procedure to the Hamiltonian to obtain the Wheeler-DeWitt equation. Solving the Wheeler-DeWitt equation and employing the de Broglie-Bohm interpretation to the wave function of the universe, we obtain a new version of spatially flat Friedmann equation for the early universe where the scale factor of the universe is taken to be sufficiently small. 相似文献