共查询到20条相似文献，搜索用时 15 毫秒
1.
Equations governing the coupling of the scalar and vector potentials for a resistive electron-positron plasma in a strong magnetic field are derived. It is shown that in the presence of magnetic shear, a tearing instability may occur. The latter can lead to magnetic field line reconnection and the formation of magnetic islands which could affect the dynamics of the pulsar magnetosphere. 相似文献
2.
The scalar equations of infinitesimal elastic gravitational motion for a rotating, slightly elliptical Earth are always used
to study the Earth's nutation and tides theoretically, while the determination of the integration of the equations depends,
to a certain extent, on the choice of a set of appropriate boundary conditions. In this paper, a continuity quantity related
to the displacement is first transformed from the elliptical reference boundary to the corresponding effective spherical domain,
and then converted from a vector (or tensor) form to a scalar form by generalized surface spherical harmonics expansion. All
the related components, including the displacement vector field (or the stress tensor field), are then decomposed into the
poloidal and toroidal field using the symmetry restrictions on the normal mode eigenfunctions. After truncation, the boundary
conditions are finally derived, in a scalar ordinary differential form. The process of the derivation is second order in ellipticity
and in full detail. Moreover, the other boundary conditions are also presented as second order in ellipticity at the end of
this paper.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
Yousef Bisabr 《Astrophysics and Space Science》2014,350(1):407-411
We consider a generalized Brans-Dicke model in which the scalar field has a potential function and is also allowed to couple non-minimally with the matter sector. This anomalous gravitational coupling can in principle avoid the model to pass local gravity experiments. One then usually assumes that the scalar field has a chameleon behavior in the sense that it acquires a density-dependent effective mass. While it can take a small effective mass in cosmological (low-density environment) scale, it has a sufficiently heavy mass in Solar System (large-density environment) and then hides gravity tests. We will argue that such a chameleon behavior can not be generally realized and depends significantly on the forms attributed to the potential and the coupling functions. 相似文献
4.
L. C. Garcia de Andrade 《Astrophysics and Space Science》1992,198(1):79-83
The equivalence of Lagrangian containing gravitational, electromagnetic, scalar, and torsion fields is discussed. It is shown that the equation for the variation of the scalar field leads to a torsion wave equation generated by electromagnetic field leads to a torsion wave equation generated by electromagnetic fields. The system is proved to be equivalent to a Proca field coupling torsion non-minimally to a massive photon and having the scalar Higgs field as a strength of this photon-torsion coupling. The generalized Maxwell equations containing the scalar fields are obtained. The torsion potential around the Sun or a more massive collapsing star in the weak field limit is estimated. 相似文献
5.
Recent LHC data provides precise values of coupling constants of the Higgs field, however, these measurements do not determine its coupling with gravity. We explore this freedom to see whether Higgs field non-minimally coupled to Gauss–Bonnet term in 4-dimensions can lead to inflation generating the observed density fluctuations. We obtain analytical solution for this model and that the exit of inflation (with a finite number of e-folding) demands that the energy scale of inflation is close to Electro-weak scale. We compare the scalar and tensor power spectrum of our model with PLANCK data and discuss its implications. 相似文献
6.
The scalar field theory on the background of cosmological models with n(n ≥ 1) spaces of constant curvature is considered. We take the integrable case of Ricci flat internal spaces. The coupling between the scalar and the gravitational fields includes the minimal coupling as well as the conformal case. In the ground state of the scalar field we find the conditions for vacuum instability realized for most of the possible solutions to Einstein's equations if the coupling parameter takes appropriate values. For the excited states of the scalar field we show the induction of massive modes and discuss their properties. 相似文献
7.
This paper investigates the existence of Noether symmetries of isotropic universe model in \(f(R,T)\) gravity admitting minimal coupling of matter and scalar fields. The scalar field incorporates two dark energy models such as quintessence and phantom models. We determine symmetry generators and corresponding conserved quantities for two particular \(f(R,T)\) models. We also evaluate exact solutions and investigate their physical behavior via different cosmological parameters. For the first model, the graphical behavior of these parameters indicate consistency with recent observations representing accelerated expansion of the universe. For the second model, these parameters identify a transition form accelerated to decelerated expansion of the universe. The potential function is found to be constant for the first model while it becomes \(V(\phi )\approx \phi ^{2}\) for the second model. We conclude that the Noether symmetry generators and corresponding conserved quantities appear in all cases. 相似文献
8.
A problem of static plane symmetric metric in the perfect fluid, the mesonic massive scalar field and in their coupling is
studied in Rosen’s (1973) bimetric theory of relativity. It was found that the matter field like either perfect fluid or mesonic
massive scalar field or their coupling does not survive in bimetric theory of gravitation when the space–time is governed
by n-dimensional static plane symmetric metric. 相似文献
9.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2011,332(1):37-42
We investigate the late-time dynamics of a four-dimensional universe based on the effective action of a Brans-Dicke scalar
field in the presence of the matter source term, conformal coupling of the scalar curvature to the scalar field, a dynamical
cosmological constant and Gauss-Bonnet higher-order terms in the scalar curvature. Many new interesting features are revealed
and discussed in some details. 相似文献
10.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2011,331(1):199-206
We investigate the late-time dynamics of a four-dimensional universe based on the effective action of a Brans-Dicke scalar field in the presence of the matter source term, conformal coupling of the scalar curvature to the scalar field, a dynamical cosmological constant and Gauss-Bonnet higher-order terms in the scalar curvature. Many new interesting features are revealed and discussed in some details. 相似文献
11.
We consider a spatially homogeneous and isotropic flat Robertson-Walker model filled with a scalar (or tachyonic) field minimally
coupled to gravity in the framework of higher derivative theory. We discuss the possibility of the emergent universe with
normal and phantom scalar fields (or normal and phantom tachynoic fields) in higher derivative theory. We find the exact solution
of field equations in normal and phantom scalar fields and observe that the emergent universe is not possible in normal scalar
field as the kinetic term is negative. However, the emergent universe exists in phantom scalar field in which the model has
no time-like singularity at infinite past. The model evolves into an inflationary stage and finally admits an accelerating
phase at late time. The equation of state parameter is found to be less than −1 in early time and tends to −1 in late time
of the evolution. The scalar potential increases from zero at infinite past to a flat potential in late time. More precisely,
we discuss the particular case for phantom field in detail. We also carry out a similar analysis in case of normal and phantom
tachyonic field and observe that only phantom tachyonic field solution represents an emergent universe. We find that the coupling
parameter of higher order correction affects the evolution of the emergent universe. The stability of solutions and their
physical behaviors are discussed in detail. 相似文献
12.
In this paper it is shown that in non-minimally coupled Brans-Dicke theory containing a self-interacting potential, a suitable conformal transformation can automatically give rise to an interaction between the normal matter and the Brans-Dicke scalar field. Considering the scalar field in the Einstein frame as the quintessence matter, it has been shown that such a non-minimal coupling between the matter and the scalar field can give rise to a late time accelerated expansion for the universe preceded by a decelerated expansion for very high values of the Brans-Dicke parameter ω. We have also studied the observational constraints on the model parameters considering the Hubble and Supernova data. 相似文献
13.
E. L. Liipola 《Celestial Mechanics and Dynamical Astronomy》1974,9(4):483-489
The Pontryagin/Lawden scalar product of the deviation phase vector and the adjoint phase vector may be identified with Lagrange's reciprocal formula for two variant motions if the acceleration field is conservative. Hence for two slightly different trajectories with common end-points, the terminal velocity differences must have equal scalar product with Lawden's primer vectors. The final velocity difference is orthogonal to the constant time of flight locus for isoenergetic motions from a common initial point. A Keplerian trajectory behaves like a rigid curve as far as radial deviation is concerned in the case of a small change of direction of the initial velocity vector. 相似文献
14.
The so called gamma metric corresponds to a two‐parameter family of axially symmetric, static solutions of Einstein's equations found by Bach. It contains the Schwarzschild solution for a particular value of one of the parameters, that rules a deviation from spherical symmetry. It is shown that there is invariantly definable singular behaviour beyond the one displayed by the Kretschmann scalar when a unique, hypersurface orthogonal, timelike Killing vector exists. In this case, a particle can be defined to be at rest when its world‐line is a corresponding Killing orbit. The norm of the acceleration on such an orbit proves to be singular not only for metrics that deviate from Schwarzschild's metric, but also on approaching the horizon of Schwarzschild metric itself, in contrast to the discontinuous behaviour of the curvature scalar. 相似文献
15.
A. A. Saharian 《Astrophysics》2000,43(1):92-101
A new mechanism is proposed for stabilization of the scalar dilaton field within the framework of lowenergy string gravitation
with loop corrections to the dilaton coupling functions. It is based on the assumption that the loop corrections generate
a kinetic dilaton function, which is singular for some finite value of the dilaton field. For a nongravitational source of
the barotropic type, the system of equations describing the evolution of homogeneous and isotropic cosmological models is
represented in the form of a thirdorder, autonomous, dynamical system. The behavior of the general solution in the vicinity
of singularities of the dilaton coupling function is investigated by methods of the qualitative theory of dynamical systems.
It is shown that there is a class of solutions, different from solutions of the general theory of relativity, with a constant
dilaton. The conditions under which these solutions are an attractor for a general solution with a variable dilaton are determined.
Translated from Astrofizika, Vol. 43, No. 1, pp. 123-136, January–March, 2000. 相似文献
16.
S. Gottl
ber 《Astronomische Nachrichten》1984,305(1):1-4
The behaviour of classical massive scalar and vector fields as sources of homogeneous world models is examined. The consequence of the violation of the strong energy condition by the massive scalar field for the evolution of an cosmological model is discussed. 相似文献
17.
K.-H. Rdler 《Astronomische Nachrichten》1972,294(5):213-224
This paper deals with the mathematical treatment of special models of hydromagnetic dynamos. For the models considered here the conducting medium occupies a spherical region surrounded by vacuum. Both laminar and turbulent dynamos are included. The partial vector differential equations governing the models are transformed into an infinite set of differential equations for scalar functions by applying a method previously used by BULLARD and GELLMAN and on the basis of a representation of vector fields as a sum of a poloidal and a toroidal part. The scalar functions depend only on a radial coordinate and possibly on the time. In both the stationary and the periodic case, an infinite set of ordinary differential equations results which may be treated numerically. A series of relations for computing various dynamo models is prepared. 相似文献
18.
The polar magnetic field near the cycle minimum is known to correlate with the height of the next sunspot maximum. There is reason to believe that the hemispheric coupling can play an important role in forming the next cycle. The meridional component of the large-scale magnetic field can be one of the hemispheric coupling indices. For our analysis we have used the reconstructed data on the large-scale magnetic field over 1915–1986. We show that in several cycles not only the height but also the general course of the cycle can be described in this way about 6 years in advance. This coupling has been confirmed by the currently available data from 1976 to 2016, but the ratio of the meridional field to the total absolute value of the field vector has turned out to be a more promising parameter. In this paper it was calculated at a height of ～70 Mm above the photosphere. The date of the forthcoming minimum is estimated using this parameter to be mid-2018; using the global field as a forecast parameter gives a later date of the minimum, early 2020. 相似文献
19.
It is well known that a C-field, generated by a certain source equation leads to interesting changes in the cosmological solutions
of Einstein's equations. It is argued that different types of topological objects may have been created by the vacuum phase
transitions in the early universe. In the cosmological arena, the defects have been put forward as a possible mechanism for
structure formation. A global monopole is a heavy object formed in the phase transition of a system composed of a self coupling
scalar field triplet φa whose original global 0(3) symmetry is spontaneously broken to U(1). In this article, we find a special solution for the
space-time of a global monopole in presence of C-field. It is shown that the nature of the solution remains the same as in
general relativity case i.e. monopole exerts no gravitational force on the matter surrounding it but space around it has a
deficit solid angle.
Pacs Nos: 98.80cq, 04.20jb, 04.50 相似文献
20.
Abstract— In oblique impacts with an impact angle under 45°, the bilateral shape of the distal ejecta blanket is used as the strongest indicator for an impact vector. This bilateral symmetry is attenuated and is superimposed by radial symmetry towards the crater rim, which remains circular for impact angles down to 10–15°. The possibility that remnants of bilateral symmetry might still be present in the most proximal ejecta, the overturned flap and the crater rim was explored with the intention of deducing an impact vector. A model is presented that postulates bilateral patterns using proximal ejecta trajectories and predicts these patterns in the orientation of bedding planes in the crater rim. This model was successfully correlated to patterns described by radial grooves in the proximal ejecta blanket of the oblique Tooting crater on Mars. A new method was developed to detect structural asymmetries by converting bedding data into values that express the deviation from concentric strike orientation in the crater rim relative to the crater center, termed “concentric deviation.” The method was applied to field data from Wolfe Creek crater, Western Australia. Bedding in the overturned flap implies an impactor striking from the east, which refines earlier publications, while bedding from the inner rim shows a correlation with the crater rim morphology. 相似文献