共查询到20条相似文献，搜索用时 46 毫秒
1.
G. Venturi 《Astroparticle Physics》1993,1(4):417-428
The matter-gravity system is examined in a path integral approach for the case of conformal matter coupled to a Friedman-Robertson-Walker space time. In particular the case of gravitational potentials of interest in cosmology for which the universe tunnels from a small radius is examined. It is observed that in the presence of such gravitational horizons the universe evolves in a complex time and it is shown how a classical time and temperature emerge. Correspondingly, one will have compensating quantum and thermal fluctuations for the matter and gravity system and it is noted that the unstable mode of gravity corresponding to the universe tunneling into existence will be compensated by an analogous mode for matter corresponding to its creation. This last point is examined in a simple De Sitter model with conformal matter and a relation is found between the cosmological constant, the number of matter fields and the self coupling of matter responsable for its instability. 相似文献
2.
Antonaldo Diaferio Luisa Ostorero 《Monthly notices of the Royal Astronomical Society》2009,393(1):215-223
We run adiabatic N -body/hydrodynamical simulations of isolated self-gravitating gas clouds to test whether conformal gravity, an alternative theory to general relativity, is able to explain the properties of X-ray galaxy clusters without resorting to dark matter. We show that the gas clouds rapidly reach equilibrium with a density profile which is well fitted by a β-model whose normalization and slope are in approximate agreement with observations. However, conformal gravity fails to yield the observed thermal properties of the gas cloud: (i) the mean temperature is at least an order of magnitude larger than the observed and (ii) the temperature profiles increase with the square of the distance from the cluster centre, in clear disagreement with real X-ray clusters. These results depend on a gravitational potential whose parameters reproduce the velocity rotation curves of spiral galaxies. However, this parametrization stands on an arbitrarily chosen conformal factor. It remains to be seen whether a different conformal factor, specified by a spontaneous breaking of the conformal symmetry, can reconcile this theory with observations. 相似文献
3.
We consider a generalization of the Standard Model whose action displays conformal invariance in d dimensions. The model contains a strongly coupled dark matter sector which breaks conformal symmetry dynamically. The model evades conformal anomaly and leads to identically zero vacuum energy in flat space-time. Hence it does not suffer from the problem of fine tuning of the cosmological constant. We determine the contribution of non-relativistic matter to the energy-momentum tensor and determine a parameter regime in which it approximately reduces to the standard result. We show how dark energy and dark matter arises in this model. We discuss the parameter range for which the model reduces to the ΛCDM model and hence is consistent with observations. 相似文献
4.
We consider Brans-Dicke theory with a self-interacting potential in Einstein conformal frame. We introduce a class of solutions
in which an accelerating expansion is possible in a spatially flat universe for positive and large values of the Brans-Dicke
parameter consistent with local gravity experiments. In this Einstein frame formulation, the theory appears as an interacting
quintessence model in which the interaction term is given by the conformal transformation. In such an interacting model, we
shall show that the solutions lead simultaneously to a constant ratio of energy densities of matter and the scalar field. 相似文献
5.
A. A. Saaryan 《Astrophysics》1995,38(3):248-260
We carry out an analysis of the exact solution obtained in the first part of this work for a homogeneous and anisotropic flat cosmological model in the general conformal representation of multidimensional low-energy string theory. We show that the singular solutions with power law of variation of the scale factors of maximally symmetric subspaces and scalar field are asymptotes of the general solution in early and late stages of evolution. We study the conditions under which models of exponential, extended, and violent inflation are realized. As an illustration of the general regularities we consider the specific example of an antisymmetric Kalb-Ramond field as a gravitational source. We demonstrate the possibility of dynamic compactification of the extra dimensions.Translated fromAstrofizika, Vol. 38, No. 3, 1995. 相似文献
6.
A. A. Saaryan 《Astrophysics》1995,38(2):164-175
We consider multi-dimensional cosmological models in the low-energy field theory of strings with a boson gravitational sector containing a metric, dilaton field, and antisymmetric Kalb-Ramon field. We study the conformal properties of the action and show that in the general conformal representation the theory is equivalent to a generalized scalar-tensor theory with a Lagrangian of nongravitating matter dependent on the dilaton. We find exact solutions of the flat homogeneous anisotropic model with structure R×M1×...×Mn and with equation of state pi=ai in the space Mi. We discuss the picture of cosmological evolution in different conformal representations.Translated fromAstrofizika, Vol. 38, No. 2, 1995. 相似文献
7.
We have calculated the equation of state of the neutron star matter and some of its properties for a wide range of nucleon-nucleon
potentials using the lowest order constrained variational (LOCV) method. It turns out that for the UV
14+TNI potential, the proton fraction exhibits a peak and falls off at high densities. The equation of state with the UV
14+TNI potential is seen to be much harder than those with other potentials. The polytropic behaviour of the neutron star matter
with various potentials are discussed. Compared with the other methods, the LOCV results show good agreement for densities
below 0.7 fm
-3. Above this density, however, the differences with other methods are appreciable. 相似文献
8.
Farook Rahaman Mubasher Jamil Ranjan Sharma Kausik Chakraborty 《Astrophysics and Space Science》2010,330(2):249-256
We provide a new class of interior solutions for anisotropic stars admitting conformal motion. The Einstein’s field equations in this construction are solved for specific choices of the density/mass functions. We analyze the behavior of the model parameters like radial and transverse pressures, density and surface tension. 相似文献
9.
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
10.
11.
Mark Vogelsberger Simon D. M. White Amina Helmi Volker Springel 《Monthly notices of the Royal Astronomical Society》2008,385(1):236-254
We present a new and completely general technique for calculating the fine-grained phase-space structure of dark matter (DM) throughout the Galactic halo. Our goal is to understand this structure on the scales relevant for direct and indirect detection experiments. Our method is based on evaluating the geodesic deviation equation along the trajectories of individual DM particles. It requires no assumptions about the symmetry or stationarity of the halo formation process. In this paper we study general static potentials which exhibit more complex behaviour than the separable potentials studied previously. For ellipsoidal logarithmic potentials with a core, phase mixing is sensitive to the resonance structure, as indicated by the number of independent orbital frequencies. Regions of chaotic mixing can be identified by the very rapid decrease in the real-space density of the associated DM streams. We also study the evolution of stream-density in ellipsoidal NFW haloes with radially varying isopotential shape, showing that if such a model is applied to the Galactic halo, at least 105 streams are expected near the Sun. The most novel aspect of our approach is that general non-static systems can be studied through implementation in a cosmological N -body code. Such an implementation allows a robust and accurate evaluation of the enhancements in annihilation radiation due to fine-scale structure such as caustics. We embed the scheme in the current state-of-the-art code gadget -3 and present tests which demonstrate that N -body discreteness effects can be kept under control in realistic configurations. 相似文献
12.
We extend to study Hawking radiation via tunneling in conformal gravity. We adopt Parikh-Wilczek’s semi-classical tunneling method and the method of complex-path integral to investigate Hawking radiation from new rotating AdS black holes in conformal gravity. In this paper, the research on Hawking radiation from the rotating black holes is done in a general system, not limited in dragging coordinate systems any longer. Moreover, there existed some shortcomings in the previous derivation of geodesic equations. Different from the massless case, they used a different approach to derive the geodesic equation of the massive particles. Even the treatment was inconsistent with the variation principle of action. To remedy the shortcoming, we improve treatment to deduce the geodesic equations of massive and massless particles in a unified and self-consistent way. In addition, we also recover the Hawking temperature resorting to the complex-path integral method. 相似文献
13.
Luis Benet 《Celestial Mechanics and Dynamical Astronomy》2001,81(1-2):123-128
We consider the system of planetary rings with shepherds as a restricted three or four-body problem, neglecting interactions between ring particles. We show that the generic occurrence of rings for the case of rotating short-range potentials can be extended to the case of gravitational potentials. The consecutive collision periodic orbits created by saddle-center bifurcations are of central importance. 相似文献
14.
H. Ziaeepour 《Astrophysics and Space Science》1998,261(1-4):229-230
The method of conformal metric is used to find an analytic set of consistent initial data for the linearized Einstein field
equations. We discuss the relation between independent degrees of freedom and perturbations.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Magnetospheres, which result from a solar wind flow parallel to the magnetic dipole, are expected for Uranus at its solstitial points and perhaps for the Palaeo-Earth during the times of field reversal. We present a two-dimensional analytical model for a pole-on magnetopause and the magnetospheric magnetic field line configuration, employing a conformal mapping method. 相似文献
16.
Using the metric conformal transformation and simple path integral, Feynman propagator method, for computing its quantum fluctuations,
we analyse the radiation dominated anisotropic Bianchi Type I cosmology. We proceed to show that the quantum conformal fluctuations
diverge at the classical spacetime singularity, suggesting that a singularity free solution can exist in anisotropic cosmology
in the quantum regime.
Since the December 1998 issue of this journal was delayed, we were able to include this paper in this issue. 相似文献
17.
E. G. Mychelkin 《Astrophysics and Space Science》1991,184(2):235-245
The problem of fundamental physical constants variability is discussed on the basis of extended conformal symmetry principles including the concept of local mass variability. It is shown, in particular, that the canonical determination of conformal weights can lead, in general, to non-invariance of the known elementary charge-to-mass ratio. The introduction of active time-like and space-like conformal transformations leads also to possibility of simultaneous variations of dimensional constants without any observable changes in the evolution of the Univrse. The generally covariant method of space-time splitting for conformal renormalization of the metric is considered in terms of Lie derivatives. 相似文献
18.
Giuseppe Pucacco 《Celestial Mechanics and Dynamical Astronomy》2004,90(1-2):109-123
We study strongly and weakly integrable 2-dimensional Hamiltonian systems with velocity dependent potentials. We determine
the set of conditions which must be satisfied in order to allow the existence of an independent second invariant polynomial
in the momenta. We then investigate the linear case for which a complete solution of the problem can be obtained. We recover
the classical set of linear strongly integrable systems and provide several new examples of weakly integrable systems whose
equations of motion can be explicitly solved at a fixed value of the energy. 相似文献
19.
O. Kaburaki 《Astrophysics and Space Science》1985,112(1):157-174
A theoretical scheme is developed to deal with the problems of stellar winds in three-dimensional situations, and relativistic fluid equations are integrated formally under isentropic and quasi-stationary conditions, in a flat space-time.The relativistic Euler equation for a one-component plasma is expressed in the same form as the ideal-MHD condition for the effective electromagnetic field which combines the inertial and pressure terms with the true electromagnetic field. This equation and that of mass continuity are integrated formally by introducing Euler-type potentials for the effective magnetic field and for the mass flux in the rotating frame, respectively. Functional form of one of these Euler potentials, which represents the total energy per unit charge in the rotating frame, is specified as an integral of motion. For an electron-proton plasma, the integrals for both components are combined to yield the energy integral of the plasma as a whole and the integrated Ohm's law, in the limit of vanishing mass ratio of an electron to a proton.Maxwell's equations are divided in two parts: i.e., the co-rotational and non-corotational parts. It is shown that the electromagnetic potentials for these parts are derived from a scalar super-potential and a vector super-potential, respectively. 相似文献
20.
Wolfgang Zwingmann 《Solar physics》1987,111(2):309-331
We apply the model of quasistatic equilibrium sequences to describe the time development of magnetic field structures in the plasma of the solar corona, and to determine onset points of a dynamical evolution. The representation of the magnetic field by Euler potentials provides a realistic modeling of the photospheric boundary conditions. We present a numerical method suited for the computation of magnetohydrodynamic equilibrium states and for analysing their stability against perturbations within ideal MHD. Pressure and magnetic footpoint displacement can be prescribed separately as boundary conditions. We consider magnetic arcade structures typical for large two-ribbon flares. Our results indicate that a finite pressure gradient seems to be essential for the existence of onset points. Furthermore, it is shown that magnetic shear destabilizes for intermediate values, but can have a stabilizing effect for a large amount of shear. 相似文献