Hasil untuk "gr-qc"

E. Paradis, Thierry Gosselin, N. Grünwald et al.

I. Arraut

Here I develop the simplest method in order to evaluate whether or not the Vainshtein mechanism can operate for a given set of parameters in a given solution. The method is based on the formulation of the mechanism in terms of the St\"uckelberg functions given in Int.J.Mod.Phys. D24 (2015) 1550022 and arXiv:1305.0475 [gr-qc]. In such a case, the Vainshtein scale appears as an extremal condition of the dynamical metric. If we fix the graviton mass, we can define the effective Vainshtein scale. Then for parameters where the Vainshtein scale vanishes or becomes smaller than the gravitational radius, the mechanism should be absent. At the other extreme, if the Vainshtein scale is finite or infinite, then the mechanism can operate. For consistency, if we define the Vainshtein scale as an invariant, then we should expect the effective graviton mass to become very large when the Vainshtein mechanism operates. On the other hand, if the mass scale tends to zero, then the extra-degrees of freedom are free to propagate. For clarity, here I analyze the effective mass behavior for the different type of modes.

A. Y. Shaikh, K. Wankhade

Jian Gao, Fang-Wei Fu, Ling Xiao et al.

E. Lashin

We examine in detail the cosmology based on quantal (Bohmian) trajectories as suggested in a recent study arXiv:1404.3093[gr-qc]. We disagree with the conclusions regarding predicting the value of the cosmological constant $\Lambda$ and evading the big bang singularity. Furthermore, we show that the approach of using a quantum corrected Raychaudhuri equation (QRE), as suggested in arXiv:1404.3093[gr-qc], is unsatisfactory, because, essentially, it uses the Raychaudhuri equation, which is a kinematical equation, in order to predict dynamics. In addition, even within this inconsistent framework, the authors have adopted unjustified assumptions and carried out incorrect steps leading to doubtful conclusions.

V. Chirde, S. Shekh

M. Azreg-Aïnou

A. N. Makarenko

We study accelerating dynamics from Born-Infeld-f(R) gravity in a simplified conformal approach without matter. In Makarenko et al. (arXiv:1404.2850 [gr-qc], 2011b) it was derived eventually any Dark Energy cosmology from above theory. In this Letter we apply the technique of Makarenko et al. (arXiv:1404.2850 [gr-qc], 2011b) to show that Born-Infeld-f(R) gravity may describe very realistic universe admitting the unification of early-time inflation with late-time acceleration. Specifically, the evolution with periodic as well as non-periodic behavior is considered with possibility to cross the phantom-divide at early or late-times.

P. Avelino, A. Hamilton, C. Herdeiro et al.

We study the geometry inside the event horizon of perturbed D dimensional Reissner-Nordstrom-(A)dS type black holes showing that, similarly to the four dimensional case, mass inflation also occurs for D>4. First, using the homogeneous approximation, we show that an increase of the number of spatial dimensions contributes to a steeper variation of the metric coefficients with the areal radius and that the phenomenon is insensitive to the cosmological constant in leading order. Then, using the code reported in arXiv:0904.2669 [gr-qc] adapted to D dimensions, we perform fully non-linear numerical simulations. We perturb the black hole with a compact pulse adapting the pulse amplitude such that the relative variation of the black hole mass is the same in all dimensions, and determine how the black hole interior evolves under the perturbation. We qualitatively confirm that the phenomenon is similar to four dimensions as well as the behaviour observed in the homogeneous approximation. We speculate about the formation of black holes inside black holes triggered by mass inflation, and about possible consequences of this scenario.

Dmitry Nesterov, S. Solodukhin

Reformulating our recent result (arXiv:1007.1246 [hep-th]) in coordinate space we point out that no matter how regular is short-distance behavior of Green’s function the entanglement entropy in the corresponding quantum field theory is always UV divergent. In particular, we discuss a recent example by Padmanabhan (arXiv:1007.5066 [gr-qc]) of a regular Green’s function and show that provided this function arises in a field theory the entanglement entropy in this theory is UV divergent and calculate the leading divergent term.

Kris Krogh

In a recent analysis of orbital data from the Mars Global Surveyor spacecraft, Iorio (2006 Class. Quantum Grav. 23 5451) found compelling evidence of general relativity's gravitomagnetic frame dragging effect. (A subsequent paper (Iorio L 2007 Preprint gr-qc/0701042v5) using the same data and equations claims agreement within 0.5% accuracy, exceeding that expected from NASA's Gravity Probe B.) However, this confirmation of general relativity was obtained by misinterpreting the MGS data and then altering a key time period.

Sean A. Hayward

Hellaby & Dray (gr-qc/9404001) have recently claimed that matter conservation fails under a change of signature, compounding earlier claims that the standard junction conditions for signature change are unnecessary. In fact, if the field equations are satisfied, then the junction conditions and the conservation equations are satisfied. The failure is rather that the authors did not make sense of the field equations and conservation equations, which are singular at a change of signature.

C. Barceló, M. Visser

We consider the case of a generic braneworld geometry in the presence of one or more moduli fields (e.g. the dilaton) that vary throughout the bulk spacetime. Working in an arbitrary conformal frame, using the generalized junction conditions of gr-qc/0008008 and the Gauss-Codazzi equations, we derive the effective ``induced'' on-brane gravitational equations. As usual in braneworld scenarios, these equations do not form a closed system in that the bulk can exchange both information and stress-energy with the braneworld. We work with an arbitrary number of moduli fields described by an arbitrary sigma model, with arbitrary curvature couplings, arbitrary self interactions, and arbitrary dimension for the bulk. (The braneworld is always codimension one.) Among the novelties we encounter are modifications of the on-brane stress-energy conservation law, anomalous couplings between on-brane gravity and the trace of the on-brane stress-energy tensor, and additional possibilities for modifying the on-brane effective cosmological constant. After obtaining the general stress-energy ``conservation'' law and the ``induced Einstein equations'' we particularize the discussion to two particularly attractive cases: for a (n−2)-brane in ([n−1] + 1) dimensions we discuss both the effect of (1) generic variable moduli fields in the Einstein frame, and (2) the effect of a varying dilaton in the string frame.

Louis Crane, D. Yetter

The purpose of this note is to make several advances in the interpretation of the balanced state sum model by Barrett and Crane in gr-qc/9709028 as a quantum theory of gravity. First, we outline a shortcoming of the definition of the model in pointed out to us by Barrett and Baez in private communication, and explain how to correct it. Second, we show that the classical limit of our state sum reproduces the Einstein-Hilbert lagrangian whenever the term in the state sum to which it is applied has a geometrical interpretation. Next we outline a program to demonstrate that the classical limit of the state sum is in fact dominated by terms with geometrical meaning. This uses in an essential way the alteration we have made to the model in order to fix the shortcoming discussed in the first section. Finally, we make a brief discussion of the Minkowski signature version of the model.

P. Bizoń, T. Chmaj

In a recent paper (gr-qc/9903081) Choptuik, Hirschmann, and Marsa have discovered the scaling law for the lifetime of an intermediate attractor in the formation of n=1 colored black holes via fine tuning. We show that their result is in agreement with the prediction of linear perturbation analysis. We also briefly comment on the dependence of the mass gap across the threshold on the radius of the event horizon.

P. Boonserm, M. Visser, S. Weinfurtner

The Tolman–Oppenheimer–Volkov [TOV] equation constrains the internal structure of general relativistic static perfect fluid spheres. We develop several “solution generating” theorems for the TOV equation, whereby any given solution can be “deformed” into a new solution. Because the theorems we develop work directly in terms of the physical observables — pressure profile and density profile — it is relatively easy to check the density and pressure profiles for physical reasonableness. This work complements our previous article [Phys. Rev. D71 (2005) 124307; gr-qc/0503007] wherein a similar “algorithmic” analysis of the general relativistic static perfect fluid sphere was presented in terms of the spacetime geometry — in the present analysis the pressure and density are primary and the spacetime geometry is secondary. In particular, our “deformed” solutions to the TOV equation are conveniently parameterized in terms of δρ c and δp c , the finite shift in the central density and central pressure. We conclude by presenting a new physical and mathematical interpretation for the TOV equation — as an integrability condition on the density and pressure profiles.

P. Wesson

The Campbell-Magaard theorem is widely seen as a way of embedding Einstein's 4D theory of general relativity in a 5D theory of the Kaluza-Klein type. We give a brief history of theorem, present a short account of it, and show that it provides a geometrical frame for new physics related to the unification of the forces. Anderson's recent vituperative attack on Campbell's theorem (gr-qc/0409122)is errant.

Andrzej Okołów, J. Lewandowski

T. Hertog, G. Horowitz, Kengo Maeda

We reexamine our proposed counterexample (gr-qc/0307102) to cosmic censorship in anti de Sitter (AdS) space, and find a gap in the construction. We mention some possible ways to close the gap, but at present the question of whether cosmic censorship is violated in AdS remains open.

A. Rostworowski

We adopt Leaver's method to determine quasi normal frequencies of the Schwarzschild black hole in higher (D >= 10) dimensions. In D-dimensional Schwarzschild metric, when D increases, more and more singularities, spaced uniformly on the unit circle |r|=1, approach the horizon at r = r_h = 1. Thus, a solution satisfying the outgoing wave boundary condition at the horizon must be continued to some mid point and only then the continued fraction condition can be applied. This prescription is general and applies to all cases for which, due to regular singularities on the way from the point of interest to the irregular singularity, Leaver's method in its original setting breaks down. We illustrate the method calculating gravitational vector and tensor quasinormal frequencies of the Schwarzschild black hole in D=11 and D=10 dimensions. We also give the details for the D=9 case, considered in gr-qc/0511064.