共查询到20条相似文献,搜索用时 46 毫秒
1.
A. Palit A. Panchenko N. G. Migranov A. Bhadra K. K. Nandi 《International Journal of Theoretical Physics》2009,48(5):1271-1289
Phase space method provides a novel way for deducing qualitative features of nonlinear differential equations without actually
solving them. The method is applied here for analyzing stability of circular orbits of test particles in various physically
interesting environments. The approach is shown to work in a revealing way in Schwarzschild spacetime. All relevant conclusions
about circular orbits in the Schwarzschild-de Sitter spacetime are shown to be remarkably encoded in a single parameter. The analysis in the rotating Kerr black hole readily exposes information as to how stability depends on the ratio
of source rotation to particle angular momentum. As a wider application, it is exemplified how the analysis reveals useful
information when applied to motion in a refractive medium, for instance, that of optical black holes. 相似文献
2.
3.
WANG Jun WANG Yong-Jiu 《理论物理通讯》2006,46(12)
In this paper the generalized equations for spinning space are investigated and the constants of motion are derived in terms of the solutions of these equations. We study the geodesic motion of the pseudo-classical spinning particles in the spacetime produced by an idealized cosmic string and the non-extreme stationary axisymmetric black hole spacetime. The bound state orbits in a plane are discussed. We also show, for a conical spacetime and the Kerr spacetime, that the geodesic motion of spinning particles is different. 相似文献
4.
The regular and chaotic dynamics of test particles in a superposed field between a pseudo-Newtonian Kerr black hole and quadrupolar halos is detailed.In particular,the dependence of dynamics on the quadrupolar parameter of the halos and the spin angular momentum of the rotating black hole is studied.It is found that the small quadrupolar moment,in contrast with the spin angular momentum,does not have a great effect on the stability and radii of the innermost stable circular orbits of these test particles.In addition,chaos mainly occurs for small absolute values of the rotating parameters,and does not exist for the maximum counter-rotating case under some certain initial conditions and parameters.This means that the rotating parameters of the black hole weaken the chaotic properties.It is also found that the counter-rotating system is more unstable than the co-rotating one.Furthermore,chaos is absent for small absolute values of the quadrupoles,and the onset of chaos is easier for the prolate halos than for the oblate ones. 相似文献
5.
WANG Jun WANG Yong-Jiu 《理论物理通讯》2006,46(6):995-1000
In this paper the generalized equations for spinning space are investigated and the constants of motion are derived in terms of the solutions of these equations. We study the geodesic motion of the pseudo-classical spinning particles in the spacetime produced by an idealized cosmic string and the non-extreme stationary axisymmetric black hole spacetime. The bound state orbits in a plane are discussed. We also show, for a conical spacetime and the Kerr spacetime, that the geodesic motion of spinning particles is different. 相似文献
6.
Using approximate symmetry methods for differential equations we have investigated the exact and approximate symmetries of a Lagrangian for the geodesic equations in the Kerr spacetime. Taking Minkowski spacetime as the exact case, it is shown that the symmetry algebra of the Lagrangian is 17 dimensional. This algebra is related to the 15 dimensional Lie algebra of conformal isometries of Minkowski spacetime. First introducing spin angular momentum per unit mass as a small parameter we consider first-order approximate symmetries of the Kerr metric as a first perturbation of the Schwarzschild metric. We then consider the second-order approximate symmetries of the Kerr metric as a second perturbation of the Minkowski metric. The approximate symmetries are recovered for these spacetimes and there are no non- trivial approximate symmetries. A rescaling of the arc length parameter for consistency of the trivial second-order approximate symmetries of the geodesic equations indicates that the energy in the charged-Kerr metric has to be rescaled and the rescaling factor is r-dependent. This re-scaling factor is compared with that for the Reissner–Nordström metric. 相似文献
7.
G. Contopoulos 《General Relativity and Gravitation》1984,16(1):43-70
We study the positions of orbits around a Kerr black hole with respect to its ergosphere. Ther– motions of zero-energy (E=0) null geodesies are inside truncated circular sectors, whose outer corners are on the static limit. Timelike geodesies with the same constants of motion are restricted inside a smaller area. For certain parameter values there are also orbits inside the inner horizon not reaching the center. Then we study the various types of orbits on the plane of symmetry for all the values of the angular momentum of the black hole 0aM, and of the angular momentum of the photons, or particles,L, and for all the values of the energyE. In particular we find the possible positions of the turning points with respect to the ergosphere. A restriction imposed by physical considerations is that the coordinate time increases when the proper time increases. This allows us to distinguish between positive and negative energy orbits. All negative energy orbits enter the horizon of the black hole. 相似文献
8.
《Physics letters. A》1998,244(5):324-328
The occurrence of chaos for test particles moving in a Taub-NUT spacetime with a dipolar halo perturbation is studied using Poincaré sections. We find that the NUT parameter (magnetic mass) attenuates the presence of chaos. 相似文献
9.
Spacetime is expected to have a “foamlike” structure on scales of the Planck length or less with high curvatures and complicated topology. This foam can be thought of as being built out of three basic kinds of units or “gravitational bubbles”, CP2, S2 × S2 and K3. We investigate the propagation of particles in simple models of the first two types of bubble. The non-trivial topologies of the bubbles introduce extra singularities into the Green functions. These make large contributions to the S-matrix for scalar particles but only small contributions for or 1 particles at energies small compared to the Planck length. These results suggest that there is no inconsistency between the spacetime foam picture and everyday observations from which spacetime appears nearly flat, because all the elementary particles we have observed have spin or greater. They do, however, suggest that Higgs scalar fields, if they exist at all, are probably bound states of higher spin particles rather than being elementary fields. Further developments may enable one to calculate processes in which quantum coherence is lost and intrinsic entropy is produced. 相似文献
10.
11.
Thorne and Kidder give expressions which allow for analytical estimates of the “kick”, i.e. the recoil, produced from asymmetrical
gravitational radiation during the interaction of black holes, or in fact any gravitating compact bodies. (The Thorne-Kidder
formula uses momentum flux calculations based on the linearized General Relativity of gravitational radiation). We specifically
treat kicks arising in the binary interaction of equal mass black holes, when at least one of the black holes has significant
spin, a. Such configurations can produce very large kicks in computational simulations. We consider both fly-by and quasicircular orbits. For fly-by orbits we find substantial kicks from those Thorne-Kidder terms which are linear in a. For the quasi-circular case, we consider in addition the nonlinear contribution (O(a
2)) to the kicks, and provide a dynamical explanation for such terms discovered and displayed by [2]. However, in the cases
of maximal kick velocities, the dependence on spin is largely linear (reproduced in numerical results [6]). 相似文献
12.
L. Siurakshina B. Paulus V. Yushankhai 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(4):445-450
Two types of oxygen-deficient perovskites RBaCo2O5.5(R=Ho,Gd) related to the “122” type structure (a
p
× 2a
p
× 2a
p
) have been studied on the basis of ab initio cluster calculations. We consider the peculiar behavior of the trivalent ions
Co3+(3d
6) in either octahedral or pyramidal oxygen coordinations, which is related to a structural first-order phase transition in
both compounds. Relative energy positions of low spin (LS, S = 0), intermediate spin (IS, S = 1) and high spin (HS, S = 2) electron configurations are calculated for the low-and high-temperature lattice structures of RBaCo2O5.5. A combined analysis of the calculated results and experimental structural data leads to a simple model that captures the
most prominent features of the phase transition common to both compounds. 相似文献
13.
The entropy density, energy density, pressure and equation of state for the gases of massless particles with spin s ≤ 2 around the static spherical black hole with quintessence are investigated by using the brick-wall method. It is shown
that the state equations for spin fields in curved spacetime do not take the same forms as that in flat spacetime and contain
additional terms with spin dependence. Then the character of the terms and the effect of quintessence and spin on them are
discussed. 相似文献
14.
We discuss some new metrics of special holonomy, and their roles in string theory and M-theory. First we consider Spin(7) metrics denoted by
, which are complete on a complex line bundle over
. The principal orbits are S7, described as a triaxially squashed S3 bundle over S4. The behaviour in the S3 directions is similar to that in the Atiyah–Hitchin metric, and we show how this leads to an M-theory interpretation with orientifold D6-branes wrapped over S4. We then consider new G2 metrics which we denote by
, which are complete on an
bundle over T1,1, with principal orbits that are S3×S3. We study the
metrics using numerical methods, and we find that they have the remarkable property of admitting a U(1) Killing vector whose length is nowhere zero or infinite. This allows one to make an everywhere non-singular reduction of an M-theory solution to give a solution of the type IIA theory. The solution has two non-trivial S2 cycles, and both carry magnetic charge with respect to the R–R vector field. We also discuss some four-dimensional hyper-Kähler metrics described recently by Cherkis and Kapustin, following earlier work by Kronheimer. We show that in certain cases these metrics, whose explicit form is known only asymptotically, can be related to metrics characterised by solutions of the su(∞) Toda equation, which can provide a way of studying their interior structure. 相似文献
15.
16.
B. S. Ramachandra 《General Relativity and Gravitation》2009,41(12):2757-2770
The existence of the Carter constant in the Vaidya–Einstein–Kerr (VEK) spacetime and its relation to the Petrov type is investigated.
This spacetime is an example of a black hole in an asymptotically non-flat background. We construct the Carter constant and
obtain the Killing tensor in the VEK spacetime. The Newman–Penrose formalism is employed to obtain the spin coefficients.
We present a complete (Petrov) classification of the VEK spacetime and the special case of the non-rotating Vaidya–Einstein–Schwarzschild
spacetime. We demonstrate explicitly that both spacetimes are of type-D. 相似文献
17.
Petr Slaný Miroslava Pokorná Zdeněk Stuchlík 《General Relativity and Gravitation》2013,45(12):2611-2633
Equatorial circular orbits of test particles in the Kerr–anti-de Sitter black-hole and naked-singularity spacetimes are analyzed and their properties like the existence, orientation and stability are discussed. Due to the attractive cosmological constant ( $\varLambda <0$ ), all particles moving along equatorial orbits are still bound in the gravitational field of the central object. In general, there are two families of equatorial circular orbits. Particles moving along minus-family orbits possess negative angular momentum and, thus, they are counterrotating from the point of view of the locally non-rotating frames (LNRF). Particles moving along plus-family orbits possess, in most cases, positive angular momentum and belong to corotating particles from the point of view of the LNRF. Nevertheless, in stationary regions inside black holes and also near naked singularities with appropriately chosen value of the cosmological constant and rotational parameter $a<1.299$ , there are also counterrotating plus-family circular orbits. Moreover, in spacetimes with $a<1.089$ , some of these orbits are characterized by negative specific energy, indicating the bounding energy of the particle, moving along such an orbit, higher than its rest energy. In black-hole spacetimes, all such orbits are radially unstable, but in naked-singularity spacetimes, stable counterrotating orbits with negative specific energy exist. 相似文献
18.
We study the covariantly constant Savvidy-type chromomagnetic vacuum in finite-temperature Yang-Mills theory on the four-dimensional
curved spacetime. Motivated by the fact that a positive spatial curvature acts as an effective gluon mass we consider the
compact Euclidean spacetime S
1 × S
1 × S
2, with the radius of the first circle determined by the temperature a
1 = (2π
T)−1. We show that covariantly constant Yang-Mills fields on S
2 cannot be arbitrary but are rather a collection of monopole-antimonopole pairs. We compute the heat kernels of all relevant
operators exactly and show that the gluon operator on such a background has negative modes for any compact semi-simple gauge
group. We compute the infrared regularized effective action and apply the result for the computation of the entropy and the
heat capacity of the quark-gluon gas. We compute the heat capacity for the gauge group SU(2N) for a field configuration of N monopole-antimonopole pairs. We show that in the high-temperature limit the heat capacity per unit volume is well defined
in the infrared limit and exhibits a typical behavior of second-order phase transition ~ (T-Tc)-3/2{\sim(T-T_c)^{-3/2}} with the critical temperature T
c
= (2π
a)−1, where a is the radius of the 2-sphere S
2. 相似文献
19.
Rotating black holes in the brany universe of the Randall–Sundrum type with infinite additional dimension are described by
the Kerr geometry with a tidal charge b representing the interaction of the brany black hole and the bulk spacetime. For b < 0 rotating black holes with dimensionless spin a > 1 are allowed. We investigate the role of the tidal charge in the orbital resonance model of quasiperiodic oscillations
(QPOs) in black hole systems. The orbital Keplerian frequency v
K and the radial and vertical epicyclic frequencies v
r, v
θ
of the equatorial, quasicircular geodetical motion are given. Their radial profiles related to Keplerian accretion discs
are discussed, assuming the inner edge of the disc located at the innermost stable circular geodesic. For completeness, naked
singularity spacetimes are considered too. The resonant conditions are given in three astrophysically relevant situations:
for direct (parametric) resonances of the oscillations with the radial and vertical epicyclic frequencies, for the relativistic
precession model, and for some trapped oscillations of the warped discs, with resonant combinational frequencies involving
the Keplerian and radial epicyclic frequencies. It is shown, how the tidal charge could influence matching of the observational
data indicating the 3 : 2 frequency ratio observed in GRS 1915 + 105 microquasar with prediction of the orbital resonance
model; limits on allowed range of the black hole parameters a and b are established. The “magic” dimensionless black hole spin enabling presence of strong resonant phenomena at the radius,
where v
K: v
θ
: v
r = 3 : 2 : 1, is determined in dependence on the tidal charge. Such strong resonances could be relevant even in sources with
highly scattered resonant frequencies, as those expected in Sgr A*. The specific values of the spin and tidal charge are given
also for existence of specific radius where v
K : v
θ
: v
r = s : t : u with 5≥s >t >u being small natural numbers. It is shown that for some ratios such situation is impossible in the field of black holes. We
can conclude that analysing the microquasars high-frequency QPOs in the framework of orbital resonance models, we can put
relevant limits on the tidal charge of brany Kerr black holes. 相似文献
20.
Zhong Chao Wu 《General Relativity and Gravitation》2006,38(2):381-386
In the Kaluza-Klein model with a cosmological constant Λ and a flux, the external spacetime of the created universe from aS
s
× S
n−s
seed instanton can be identified in quantum cosmology. One can also show that in the internal space theeffective cosmological
constant is most probably zero. 相似文献