共查询到20条相似文献,搜索用时 15 毫秒
1.
-monopoles are solutions to gauge theoretical equations on noncompact -manifolds of holonomy. We shall study this equation on the Bryant–Salamon manifolds. We construct examples of -monopoles on two of these manifolds, namely the total space of the bundle of anti-self-dual two forms over the and . These are the first nontrivial examples of -monopoles.Associated with each monopole there is a parameter , known as the mass of the monopole. We prove that under a symmetry assumption, for each given there is a unique monopole with mass . We also find explicit irreducible -instantons on and on .The third Bryant–Salamon -metric lives on the spinor bundle over the -sphere. In this case we produce a vanishing theorem for monopoles. 相似文献
2.
We consider effective actions of the cosmological Friedmann–Robertson–Walker (FRW) models and discuss their fermionic rigid BRST invariance. Further, we demonstrate the finite field-dependent BRST transformations as a limiting case of continuous field-dependent BRST transformations described in terms of continuous parameter κ. The Jacobian under such finite field-dependent BRST transformations is computed explicitly, which amounts an extra piece in the effective action within functional integral. We show that for a particular choice of a parameter the finite field-dependent BRST transformation maps the generating functional for FRW models from one gauge to another. 相似文献
3.
《Journal of Geometry and Physics》2001,37(3):229-236
We prove that a Sasakian 3-manifold admitting a non-trivial solution to the Einstein–Dirac equation has necessarily constant scalar curvature. In the case when this scalar curvature is non-zero, their classification follows then from a result by Th. Friedrich and E.C. Kim. We also prove that a scalar-flat Sasakian 3-manifold admits no local Einstein spinors. 相似文献
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5.
Sergey S. Kokarev 《General Relativity and Gravitation》2009,41(8):1777-1794
Cosmological singularity and asymptotic behavior of scale factor of generalized cosmological models are analyzed in respect
of their structural stability. It is shown, that cosmological singularity is structurally unstable for the majority of models
with barotropic perfect fluid with strong energy condition. Inclusion of Λ-term extends the set of structurally stable cosmological
models. 相似文献
6.
Abhas Mitra 《General Relativity and Gravitation》2010,42(3):443-469
Following Einstein’s definition of Lagrangian density and gravitational field energy density (Einstein in Ann Phys Lpz 49:806, 1916, Einstein in Phys Z 19:115, 1918, Pauli in Theory of Relativity, B.I. Publications, Mumbai, 1963), Tolman derived a general formula for the total matter plus gravitational field energy (P 0) of an arbitrary system (Tolman in Phys Rev 35:875, 1930, Tolman in Relativity, Thermodynamics &; Cosmology, Clarendon Press, Oxford, 1962, Xulu in hep-th/0308070, 2003). For a static isolated system, in quasi-Cartesian coordinates, this formula leads to the well known result \({P_0 = \int \sqrt{-g} (T_0^0 - T_1^1 - T_2^2 - T_3^3) d^3 x,}\) where g is the determinant of the metric tensor and \({T^a_b}\) is the energy momentum tensor of the matter. Though in the literature, this is known as “Tolman Mass”, it must be realized that this is essentially “Einstein Mass” because the underlying pseudo-tensor here is due to Einstein. In fact, Landau–Lifshitz obtained the same expression for the “inertial mass” of a static isolated system without using any pseudo-tensor at all and which points to physical significance and correctness of Einstein Mass (Landau, Lifshitz in The Classical Theory of Fields, Pergamon Press, Oxford, 1962)! For the first time we apply this general formula to find an expression for P 0 for the Friedmann–Robertson–Walker (FRW) metric by using the same quasi-Cartesian basis. As we analyze this new result, it transpires that, physically, a spatially flat model having no cosmological constant is preferred. Eventually, it is seen that conservation of P 0 is honoured only in the static limit. 相似文献
7.
We study the dynamics of spatially homogeneous and isotropic spacetimes containing a fluid undergoing microscopic velocity diffusion in a cosmological scalar field. After deriving a few exact solutions of the equations, we continue by analyzing the qualitative behavior of general solutions. To this purpose we recast the equations in the form of a two dimensional dynamical system and perform a global analysis of the flow. Among the admissible behaviors, we find solutions that are asymptotically de-Sitter both in the past and future time directions and which undergo accelerated expansion at all times. 相似文献
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We show that the non-Hermitian Black–Scholes Hamiltonian and its various generalizations are η-pseudo Hermitian. The metric operator η is explicitly constructed for this class of Hamiltonians. It is also shown that the effective Black–Scholes Hamiltonian and its partner form a pseudo supersymmetric system. 相似文献
10.
Fulvio Melia 《Frontiers of Physics》2017,12(1):129802
Many cosmological measurements today suggest that the Universe is expanding at a constant rate. This is inferred from the observed age versus redshift relationship and various distance indicators, all of which point to a cosmic equation of state (EoS) p = -ρ/3, where ρ and p are, respectively, the total energy density and pressure of the cosmic fluid. It has recently been shown that this result is not a coincidence and simply confirms the fact that the symmetries in the Friedmann–Robertson–Walker (FRW) metric appear to be viable only for a medium with zero active mass, i.e., ρ + 3p = 0. In their latest paper, however, Kim, Lasenby and Hobson (2016) have provided what they believe to be a counter argument to this conclusion. Here, we show that these authors are merely repeating the conventional mistake of incorrectly placing the observer simultaneously in a comoving frame, where the lapse function gtt is coordinate dependent when ρ + 3p ≠ 0, and a supposedly different, freefalling frame, in which gtt = 1, implying no time dilation. We demonstrate that the Hubble flow is not inertial when ρ + 3p ≠ 0, so the comoving frame is generally not in free fall, even though in FRW, the comoving and free-falling frames are supposed to be identical at every spacetime point. So this confusion of frames not only constitutes an inconsistency with the fundamental tenets of general relativity but, additionally, there is no possibility of using a gauge transformation to select a set of coordinates for which gtt = 1 when ρ + 3p ≠ 0. 相似文献
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Fulvio Melia 《Frontiers of Physics》2016,11(4):119801
Modern cosmological theory is based on the Friedmann–Robertson–Walker (FRW) metric. Often written in terms of co-moving coordinates, this well-known solution to Einstein’s equations owes its elegant and highly practical formulation to the cosmological principle and Weyl’s postulate, upon which it is founded. However, there is physics behind such symmetries, and not all of it has yet been recognized. In this paper, we derive the FRW metric coefficients from the general form of the spherically symmetric line element and demonstrate that, because the co-moving frame also happens to be in free fall, the symmetries in FRW are valid only for a medium with zero active mass. In other words, the spacetime of a perfect fluid in cosmology may be correctly written as FRW only when its equation of state is ρ+3p = 0, in terms of the total pressure p and total energy density ρ. There is now compelling observational support for this conclusion, including the Alcock–Paczy´nski test, which shows that only an FRW cosmology with zero active mass is consistent with the latest model-independent baryon acoustic oscillation data. 相似文献
13.
Mechanical properties of the thermal equilibrium Friedmann–Robertson–Walker universe model 下载免费PDF全文
The mechanical property of the thermal-equilibrium Friedmann-Robertson-Walker (TEFRW) universe is first studied. The equation of state and the scale factor of the TEFRW universe take the forms ofw = w(a;zT) and a = a(a;zT,Ho). For the universe consisting of the nonrelativistic matter and the dark energy, the behavior of the dark energy depends on the value of the present-day matter fraction. For the TEFRW universe consisting of N ingredients, the effective temperature is introduced. Lastly, a simple TEFRW universe model is analyzed. 相似文献
14.
Recently, a Hamilton–Jacobi method beyond the semiclassical approximation in black hole physics was developed by Banerjee
and Majhi. We generalize their analysis of black holes to the case of a Friedmann–Robertson–Walker (FRW) universe. It is shown
that all the higher order quantum corrections in the single particle action are proportional to the usual semiclassical contribution.
The corrections to the Hawking-like temperature and entropy of the apparent horizon for the FRW universe are also obtained.
In the corrected entropy, the area law involves a logarithmic area correction together with the standard term with the inverse
power of the area. 相似文献
15.
Ciprian Dariescu Adrian Bodnarescu Marina–Aura Dariescu 《International Journal of Theoretical Physics》2016,55(9):4109-4123
For the Friedmann–Robertson–Walker (FRW) Universe with negative curvature, sustained by a spontaneous Z2? symmetry breaking scalar field, depending on time alone, we have derived the Einstein–Gordon system of equations. For physically relevant cases, the matter-curvature system have been numerically analyzed. 相似文献
16.
Let X be a smooth complex projective curve and S⊂X a finite subset. We show that an orthogonal or symplectic parabolic Higgs bundle on X with parabolic structure over S admits a Hermitian–Einstein connection if and only if it is polystable. 相似文献
17.
Asymptotic properties of electromagnetic waves are studied within the context of Friedmann–Robertson–Walker (FRW) cosmology. Electromagnetic fields are considered as small perturbations on the background spacetime and Maxwells equations are solved for all three cases of flat, closed and open FRW universes. The asymptotic character of these solutions is investigated and their relevance to the problem of cosmological tails of electromagnetic waves is discussed. 相似文献
18.
Tamath Rainsford 《General Relativity and Gravitation》2000,32(4):719-733
In a previous paper [9], we derived a post-Newtonian approximation to cosmology which, in contrast to former Newtonian and post-Newtonian cosmological theories, has a well-posed initial value problem. In this paper, this new post-Newtonian theory is compared with the fully general relativistic theory, in the context of the k= 0 Friedmann–Robertson–Walker cosmology. It is found that the post-Newtonian theory reproduces the results of its general relativistic counterpart, whilst the Newtonian theory does not. 相似文献
19.
Magdalena Caballero Alfonso Romero Rafael M. Rubio 《Letters in Mathematical Physics》2010,93(1):85-105
Several uniqueness and non-existence results on complete constant mean curvature spacelike surfaces lying between two slices
in certain three-dimensional generalized Robertson–Walker spacetimes are given. They are obtained from a local integral estimation
of the squared length of the gradient of a distinguished smooth function on a constant mean curvature spacelike surface, under
a suitable curvature condition on the ambient spacetime. As a consequence, all the entire bounded solutions to certain family
of constant mean curvature spacelike surface differential equations are found. 相似文献
20.
P. C. Stavrinos A. P. Kouretsis M. Stathakopoulos 《General Relativity and Gravitation》2008,40(7):1403-1425
A generalized FRW model of space-time is studied, taking into consideration the anisotropic structure of fields which are
depended on the position and the direction (velocity). The Raychaudhouri and Friedman-like equations are investigated assuming
the Finslerian character of space-time. A long range vector field of cosmological origin is considered in relation to a physical
geometry where the Cartan connection has a fundamental role. The Friedman equations are produced including extra anisotropic
terms. The variation of anisotropy z
t
is expressed in terms of the Cartan torsion tensor of the Finslerian manifold. A physical generalization of the Hubble and
other cosmological parameters arises as a direct consequence of the equations of motion. 相似文献