共查询到20条相似文献,搜索用时 859 毫秒
1.
Nathan Rosen 《Foundations of Physics》1980,10(9-10):673-704
An attempt is made to remove singularities arising in general relativity by modifying it so as to take into account the existence of a fundamental rest frame in the universe. This is done by introducing a background metric γμν (in addition to gμν) describing a spacetime of constant curvature with positive spatial curvature. The additional terms in the field equations are negligible for the solar system but important for intense fields. Cosmological models are obtained without singular states but simulating the “big bang.” The field of a particle differs from the Schwarzschild field only very close to, and inside, the Schwarzschild sphere. The interior of this sphere is unphysical and impenetrable. A star undergoing gravitational collapse reaches a state in which it fills the Schwarzschild sphere with uniform density (and pressure) and has the geometry of a closed Einstein universe. Any charge present is on the surface of the sphere. Elementary particles may have similar structures. 相似文献
2.
Jai-Chan Hwang 《General Relativity and Gravitation》1998,30(4):545-553
In a class of generalized gravity theories with general couplings between the scalar field and the scalar curvature in the Lagrangian, we can describe the quantum generation and the classical evolution of both the scalar and tensor structures in a simple and unified manner. An accelerated expansion phase based on the generalized gravity in the early universe drives microscopic quantum fluctuations inside a causal domain to expand into macroscopic ripples in the spacetime metric on scales larger than the local horizon. Following their generation from quantum fluctuations, the ripples in the metric spend a long period outside the causal domain. During this phase their evolution is characterized by their conserved amplitudes. The evolution of these fluctuations may lead to the observed large scale structures of the universe and anisotropies in the cosmic microwave background radiation. 相似文献
3.
C G Tsagas 《Physical review letters》2001,86(24):5421-5424
The vector nature of magnetic fields and the geometrical interpretation of gravity introduced by general relativity guarantee a special coupling between magnetism and spacetime curvature. This magnetogeometrical interaction effectively transfers the tension properties of the field into the spacetime fabric, triggering a variety of effects with profound implications. Given the ubiquity of magnetic fields in the universe, these effects could prove critical. We discuss the nature of the magnetic-field--curvature coupling and illustrate some of its potential implications for cosmology. 相似文献
4.
Ramesh Tikekar 《Pramana》2000,55(4):623-628
The introduction of time dependence through a scale factor in a non-conformally flat static cosmological model whose spacetime
can be embedded in a five demensional flat spacetime is shown to give rise to two spherical models of universe filled with
perfect fluid acompannied with radial heat flux without any Big Bang type singularity. The first model describes an ever existing
universe which witnesses a transition from state of contraction to that of ever expansion. The second model represents a universe
oscillating between two regular states. 相似文献
5.
In the new framework of gravitational quantum field theory (GQFT) with spin and scaling gauge invariance developed in Phys. Rev. D 93 (2016) 024012-1, we make a perturbative expansion for the full action in a background field which accounts for the early inflationary universe. We decompose the bicovariant vector fields of gravifield and spin gauge field with Lorentz and spin symmetries SO(1,3) and SP(1,3) in biframe spacetime into SO(3) representations for deriving the propagators of the basic quantum fields and extract their interaction terms. The leading order Feynman rules are presented. A tree-level 2 to 2 scattering amplitude of the Dirac fermions, through a gravifield and a spin gauge field, is calculated and compared to the Born approximation of the potential. It is shown that the Newton's gravitational law in the early universe is modified due to the background field. The spin dependence of the gravitational potential is demonstrated. 相似文献
6.
In the new framework of gravitational quantum field theory(GQFT) with spin and scaling gauge invariance developed in Phys. Rev. D 93(2016) 024012-1, we make a perturbative expansion for the full action in a background field which accounts for the early inflationary universe. We decompose the bicovariant vector fields of gravifield and spin gauge field with Lorentz and spin symmetries SO(1,3) and SP(1,3) in biframe spacetime into SO(3) representations for deriving the propagators of the basic quantum fields and extract their interaction terms. The leading order Feynman rules are presented. A tree-level 2 to 2 scattering amplitude of the Dirac fermions, through a gravifield and a spin gauge field, is calculated and compared to the Born approximation of the potential. It is shown that the Newton's gravitational law in the early universe is modified due to the background field. The spin dependence of the gravitational potential is demonstrated. 相似文献
7.
Ivan Agullo 《General Relativity and Gravitation》2018,50(7):91
We compute the predictions for the power spectrum of scalar perturbations from a recent new proposal for the effective Hamiltonian of loop quantum cosmology. The model provides an attractive picture of the early cosmos, in which our classical Friedmann–Lemaître–Robertson–Walker universe emerges from a quantum phase where the spacetime curvature remains constant and of Planckian size. We compare the predictions for the cosmic microwave background with previous results obtained within loop quantum cosmology, and discuss the differences and similarities. The analysis provides an example of the way differences between quantization schemes can be translated to physical observables. 相似文献
8.
Bruce McFarland 《International Journal of Theoretical Physics》1997,36(6):1423-1433
We propose a model of our universe as a 3-sphere resting on the surface of a black hole which exists in a spacetime consisting
of four space dimensions and one time dimension. The matter and energy within our universe exist as stationary solutions to
the field equations in the Rindler coordinates just above the horizon of the black hole. Each solution may be though of as
a standing wave consisting of a wave propagating toward the horizon superposed with its time-reversed twin propagating away
from the horizon. As matter and energy from the greater five-dimensional spacetime fall into the black hole, its radius increases
and our universe expands. This mechanism of expansion allows the model to describe a universe which is older than its oldest
stars and homogeneous without inflation. It also predicts galaxy counts at high redshift which agree with observation. 相似文献
9.
Valerio Faraoni
Sebastiano Sonego
《Physics letters. A》1992,170(6):413-420The tail problem for the propagation of a scalar field is considered in a cosmological background, taking a Robertson-Walker spacetime as a specific example. The explicit radial dependence of the general solution of the Klein-Gordon equation with non-minimal coupling is derived, and the inapplicability of the standard calculation of the reflection and transmission coefficients to the study of scattering of waves by the cosmological curvature is discussed. 相似文献
10.
Generalized relativistic field equations have been derived for dynamics in a non-inertial reference frame interpreted as a
Finsler space where events are specified by both spacetime coordinates and corresponding velocities (tangent vectors). The
field equations follow in two alternative forms from exact general conservation laws derived through application of Cartan
covariant differentiation within the framework of Finsler geometry. Velocity-dependent (curvature) terms in the field equations
can account for the anisotropy of the gravitational field, together with the associated acceleration and expansion of the
universe. 相似文献
11.
K S Virbhadra 《Pramana》1993,40(4):273-275
An exact solution of Einstein’s equations is interpreted as describing the gravitational field of a tachyon in a de Sitter
universe. Switching off the cosmological constant yields the gravitational field of a tachyon in flat spacetime background. 相似文献
12.
The present article deals with solutions for a minimally coupled scalar field propagating in a static plane symmetric spacetime. The considered metric describes the curvature outside a massive infinity plate and exhibits an intrinsic naked singularity (a singular plane) that makes the accessible universe finite in extension. This solution can be interpreted as describing the spacetime of static domain walls. In this context, a first solution is given in terms of zero order Bessel functions of the first and second kind and presents a stationary pattern which is interpreted as a result of the reflection of the scalar waves at the singular plane. This is an evidence, at least for the massless scalar field, of an old interpretation given by Amundsen and Grøn regarding the behaviour of test particles near the singularity. A second solution is obtained in the limit of a weak gravitational field which is valid only far from the singularity. In this limit, it was possible to find out an analytic solution for the scalar field in terms of the Kummer and Tricomi confluent hypergeometric functions. 相似文献
13.
Ahmet M. Öztaş Michael L. Smith Jan Paul 《International Journal of Theoretical Physics》2008,47(9):2464-2478
We investigate universe expansion models as functions of emission frequency ratio decline rather than redshift z, using the latest on-line, self-consistent data from 192 supernovae. We present results for simpler and some current models
of cosmology, including those with dark energy (standard model) and a recent model correcting for the effect of a small time-dependent,
emission frequency increase with lookback. This new model, with a gentle lookback decline of the Planck constant, and the
standard model fit the data with similar confidence according to Bayesian Information Criteria. The standard model tends towards
solutions high in matter density while remaining flat, but models without dark energy tend towards dilute universes with significant
spacetime and curvature and a smaller Hubble constant. We conclude the normalized spacetime parameter, Ω
k
, should not be ignored and it includes the combined contributions of huge spacetime magnitude and curvature. 相似文献
14.
A model for the universe based on the back-reaction effects of quantum fields at finite temperature in the background of Robertson-Walker
spacetime and in the presence of a non-zero cosmological constant is constructed. We discuss the vacuum regime in the light
of the results obtained through previous studies of the back-reaction of massless quantum fields in the static Einstein universe,
and we argue that an adiabatic vacuum state and thermal equilibrium is achieved throughout this regime. Critical density is
maintained naturally from the very early stages as a consequence of back-reaction effect of the vacuum fluctuations of quantum
fields. Results show that such a model can explain many features of the early universe as well as the present universe. The
model is free from the basic problems of the standard Friedmann cosmology, and is non-singular but involves a continuous creation
of energy at a rate proportional to the size of the universe, which is lower than that suggested by the steady-state cosmology. 相似文献
15.
Valerio Faraoni 《General Relativity and Gravitation》1997,29(2):251-257
Recent theoretical work determines the correct coupling constant of a scalar field to the Ricci curvature of spacetime in general relativity. The periodicity in the redshift distribution of galaxies observed by Broadhurst et al., if genuine, determines the coupling constant in the proposed scalar field models. As a result, these observations contain important information on the problem of whether general relativity is the correct theory of gravity in the region of the universe at redshifts z < 0.5. 相似文献
16.
Ahmad Rami El-Nabulsi 《General Relativity and Gravitation》2010,42(6):1381-1398
We consider the flat anisotropic Bianchi I braneworld model of the universe within the framework of low energy effective string
action in four-dimensions including the leading order α′ terms, two-scalar fields, their interaction, non-minimal coupling of the dark-energy scalar field to the scalar curvature
and effective cosmological constant. Backward (high energy limit) and forward (low energy limit) in time analytic solutions
are derived and late-time accelerated expansion was found. It is shown that during the transition from high energy limit to
the low energy limit, the topology of the universe is changing in time: we have a transition from a (1 + 3) FRW homogenous
and isotropic spacetime dominated by radiation to a (1 + 2) spacetime sheet dominated by phantom energy while the third spatial
dimension is contracted in time. We have also found that dark matter and dark energy may be unified at early epoch in the
form of radiation fluids while the late-time dynamics is governed by phantom energy and dark energy. Many interesting features
are revealed. 相似文献
17.
L.H. Ford 《Nuclear Physics B》1982,204(1):35-44
The effect of the expansion of the universe upon the rate of decay of a massive scalar particle is investigated. In the limit of weak coupling to the spacetime curvature, an expression is given for the average decay rate of such a particle. It is shown that in general this process is not CPT invariant. Several explicit models for the expansion are considered, and the application of the results to the early universe is discussed. 相似文献
18.
We obtain an exact solution of the supergravity equations of motion in which the four-dimensional observed Universe is one of a number of colliding D3 branes in a Calabi-Yau background. The collision results in the ten-dimensional spacetime splitting into disconnected regions, bounded by curvature singularities. However, near the D3 branes the metric remains static during and after the collision. We also obtain a general class of solutions representing p-brane collisions in arbitrary dimensions, including one in which the universe ends with the mutual annihilation of a positive-tension and a negative-tension 3 brane. 相似文献
19.
M. Carmeli 《International Journal of Theoretical Physics》1987,26(1):83-89
Cawley's counterexample Lagrangian to Dirac's conjecture on dynamical systems is modified to a line element in curved spacetime, and the energy-momentum tensor corresponding to such a spacetime is found. The spacetime obtained satisfies the Einstein field equations and describes a three-dimensional matterfilled universe. It is further shown that such a universe cannot be filled up with other sources, such as a perfect fluid, a scalar field, or an electromagnetic field, without violating the Einstein field equations. 相似文献
20.
The fact that the energy densities of dark energy and matter are similar currently, known as the coincidence problem, is one of the main unsolved problems of cosmology. We present here a model in which a spatial curvature of the universe can lead to a transition in the present epoch from a matter dominated universe to a scaling dark energy dominance in a very natural way. In particular, we show that if the exponential potential of the dark energy field depends linearly on the spatial curvature density of a closed universe, the observed values of some cosmological parameters can be obtained assuming acceptable values for the present spatial curvature of the universe, and without fine tuning in the only parameter of the model. We also comment on possible variations of this model, and realistic scenarios in which it could arise. 相似文献