Hasil untuk "gr-qc"

S. Hossenfelder

Authors Hohmann and Wohlfarth have put forward a no-go theorem for bimetric gravity with positive and negative mass in arXiv:0908.3384v1 [gr-qc]. This comment shows that their no-go theorem does not apply to arXiv:0807.2838v1 [gr-qc].

M. Maziashvili

The idea of black hole remnants for RG modified Schwarzschild solution constructed in papers [hep-th/0002196; hep-th/0602159] depends essentially on the positiveness of a parameter that enters the running Newton constant. The positiveness of this parameter was established by comparing the large distance expansion of RG modified Schwarzschild solution with the Donoghue's original result about the one-loop correction to the Newtonian potential [gr-qc/9310024; gr-qc/9405057]. But since the appearance of paper [gr-qc/0207118] by Khriplovich and Kirilin it became widely appreciated that the sign of one-loop correction in Donoghue's original result is incorrect. This falsifies the argument for existence of black hole remnants in the framework of modified Schwarzschild solution construction suggested in the above papers. But most importantly the very construction of this modified Schwarzschild solution is challenged by the study of graviton radiative corrections to the Newtonian potential and running Newton constant [hep-th/0211071].

M. Maziashvili

S. Vacaru

Aditya Gilra

Recently, it was proposed that the spin-statistics connection arises due to a quantum dynamical phase involving cosmic gravity (Unnikrishnan C S, gr-qc/0406043). There it was assumed that the gravitational quantum phase accumulated on the wavefunctions of each of two identical particles undergoing scattering in the presence of cosmic matter with the direction of their momentum changing by some angle is equivalent to the particles forward scattering with the entire universe rotating oppositely by the same angle. However, if one considers the gravitational phase accumulated by an electron in orbit to be analogous to that acquired by a scattering particle, the accumulated phase inferred from the fine-structure splitting in an atom is too small to explain the spin statistics connection. Though, the desirability of a dynamical proof of the spin-statistics connection remains.

H. Culetu

It is shown that Collas and Klein (ArXiv : 0811.2471 [gr-qc]) wrongly concluded that "negative frame dragging" phenomenon takes place at all finite $r$ and $z$ coordinate values . We argue that a test particle with zero angular momentum counter-rotates with respect to the source in the "time machine" region only. In addition, Bonnor's spacetime has an event horizon at $r_{H}$ = 0.

R. Gentry

In late 1997 I reported (Mod. Phys. Lett. A 12 (1997) 2919; astro-ph/9806280) the discovery of A New Redshift Interpretation (NRI) of the Hubble relation and the 2.7K CBR, which showed for the first time that it was possible to explain these phenomena within the framework of a universe governed by Einstein's static-spacetime general relativity (GR) instead of the Friedmann-Lemaitre expanding-spacetime paradigm. More recently Carlip and Scranton (astro-ph/9808021; C&S) claim to find flaws in this discovery, while also claiming the standard cosmology is error free. Their analysis assumes the NRI represents a static cosmological model of the universe. This is wrong. My MPLA report clearly states the NRI encompasses an expanding universe wherein galaxies are undergoing Doppler recession due to vacuum density repulsion. C&S's confusion on this crucial point leads to serious errors in their analysis. Next, in claiming the standard cosmology is error free, C&S fail to respond to the contradictory evidence in my preprint, gr-qc/9806061. There I first show why the universe is governed by Einstein static-spacetime GR, and not the Friedmann-Lemaitre expanding spacetime paradigm on which Big Bang cosmology is critically hinged. Secondly, I note a most embarrassing fact about the F-L paradigm--namely, that it has always involved gargantuan nonconservation-of-energy losses amounting to the mass equivalent of about thirty million universes, each with a mass of 10^21 suns.

V. Mashkevich

This paper is a continuation of the papers [gr-qc/9409010, gr-qc/9505034, gr-qc/9603022, gr-qc/9609035, gr-qc/9609046]. The introduction of a prior, i.e., predynamical global geometry of spacetime manifold is substantiated, and the geometry is specified. The manifold is an infinite four-cylinder, or tube in the five-dimensional Euclidean space, the orthogonal section of the cylinder being the unit three-sphere. Supplementary conditions for metric are introduced geometrically, coordinate-independently, as opposed to coordinate conditions. Parity and time-reversal transformations are extended to the manifold specified. PT is equivalent to a rotation through \pi about an axis orthogonal to the cylinder axis. CPT invariance is discussed. Keywords: cosmic time, cosmic space, cylindrical manifold

V. Mashkevich

This paper is a continuation of the papers [gr-qc/9409010, gr-qc/9505034, gr-qc/9603022, gr-qc/9609035, gr-qc/9609046, gr-qc/9704033]. The aim of the paper is to incorporate singularities---both local (black hole and naked singularity) and global (big bang and big crunch)---into the dynamics of indeterministic quantum gravity and cosmology. The question is whether a singularity is dynamically passable, i.e., whether a dynamical process which ends with a singularity may be extended beyond the latter. The answer is yes. A local singularity is trivially passable, while the passableness for a global singularity may invoke CPT transformation. The passableness of the singularities implies pulsating black holes and the oscillating universe. For the local singularity, the escape effect takes place: In a vicinity of the singularity, quantum matter leaves the gravitational potential well. Keywords: tempered singularity, strong singularity, trivial passage, CPT passage, pulsating black hole, escape effect, oscillating universe

I. Kouletsis, P. Hájícek

The study of the two-shell system started in ``Pair of null gravitating shells I and II'' (gr-qc/0112060--061) is continued. The pull back of the Liouville form to the constraint surface, which contains complete information about the Poisson brackets of Dirac observables, is computed in the singular double-null Eddington-Finkelstein (DNEF) gauge. The resulting formula shows that the variables conjugate to the Schwarzschild masses of the intershell spacetimes are simple combinations of the values of the DNEF coordinates on these spacetimes at the shells. The formula is valid for any number of in- and out-going shells. After applying it to the two-shell system, the symplectic form is calculated for each component of the physical phase space; regular coordinates are found, defining it as a symplectic manifold. The symplectic transformation between the initial and final values of observables for the shell-crossing case is written down.

Cornish

Levin (gr-qc/9910040) has shown that spinning compact binaries can be chaotic at second post-Newtonian order. However, when higher order dissipational effects are included, the dynamics will no longer be chaotic, though the evolution may still be unpredictable in a practical sense. I discuss some of the additional work that needs to be done to decide how this unpredictability might affect gravitational wave detectors such as LIGO.

A. Bernal, Miguel Sánchez Caja

This paper has been withdrawn because the new one gr-qc/0512095 includes all its results (as well as those in gr-qc/0511016) in a clearer way.

F. Aquino

It has been demonstrated (gr-qc/9910036) that the gravitational and inertial masses are correlated by a dimensionless electromagnetic factor, which can be different from one. It can be also reduced, nullified or made negative in specific electromagnetic conditions. This unexpected theoretical result has been confirmed by an experiment using Extra-Low Frequency(ELF) radiation on ferromagnetic material (gr-qc/0005107). Recently another experiment using UV light on phosphorescent plastic has confirmed the phenomenon. Here we show some fundamental consequences of the correlation for the Quantum Cosmology.

B. Gato-Rivera

In the recent article ‘Conflict between anthropic reasoning and observation’ (gr-qc/0303070) Ken D. Olum, using some inflation-based ideas and the anthropic premise that we should be typical among all intelligent observers in the Universe, arrives at the puzzling conclusion that ‘we should find ourselves in a large civilization (of galactic size) where most observers should be, while in fact we do not’. In this note we discuss the intriguing possibility whether we could be in fact immersed in a large civilization without being aware of it. Our conclusion is that this possibility cannot be ruled out provided two conditions are met, that we call the Subanthropic Principle and the Undetectability Conjecture. The Subanthropic Principle states that we are not typical among the intelligent observers from the Universe. Typical civilizations of typical galaxies would be hundreds of thousands, or millions, of years more evolved than ours and, consequently, typical intelligent observers would be orders of magnitude more intelligent than us. The Undetectability Conjecture states that, generically, all advanced civilizations camouflage their planets for security reasons, so that no signal of civilization can be detected by external observers, who would only obtain distorted data for disuasion purposes. These conditions predict also a low probability of success for the SETI project. We also argue that it is brane worlds, and not inflation, what dramatically could aggravate the ‘missing-alien’ problem pointed out first in the fifties by Enrico Fermi.

C. Unnikrishnan

I suggest that the Spin-Statistics connection is a consequence of the phase shifts on quantum scattering amplitudes due to the induced gravitomagnetic field of the whole Universe at critical density. This connection was recently brought out in the context of a new theory of relativity in flat space with matter, called Cosmic Relativity (gr-qc/0406023). This prediction of the correct gravitational phases is a consequence of any relativistic gravitation theory in the presence of the massive Universe. This can also be interpreted as related to the Mach's principle applied to quantum phenomena. Perhaps this is the simplest valid proof of the Spin-Statistics Theorem, and it finally identifies the physical origin of the connection.

Scott H. Hawley, M. Choptuik

We present a brief synopsis of related work (gr-qc/0007039), describing a study of black hole threshold phenomena for a self-gravitating, massive complex scalar field in spherical symmetry. We construct Type I critical solutions dynamically by tuning a one-parameter family of initial data consisting of a boson star and a massless real scalar field, and numerically evolving this data. The resulting critical solutions appear to correspond to boson stars on the unstable branch, as we show via comparisons between our simulations and perturbation theory. For low-mass critical solutions, we find small ``halos'' of matter in the tails of the solutions, and these distort the profiles which otherwise agree with unstable boson stars. These halos seem to be artifacts of the collisions between the original boson stars and the massless fields, and do not appear to belong to the true critical solutions. From this study, it appears that unstable boson stars are unstable to dispersal (``explosion'') in addition to black hole formation. Given the similarities in macroscopic stability between boson stars and neutron stars, we suggest that similar phenomena could occur in models of neutron stars.

S. Vacaru

The 'anholonomic frame' method (see gr-qc/0005025, gr-qc/0001060 and hep-th/0110250) is applied for constructing new classes of exact solutions of vacuum Einstein equations with off-diagonal metrics in 4D and 5D gravity. We examine several black tori solutions generated by anholonomic transforms with non-trivial topology of the Schwarzshild metric, which have a static toroidal horizon. We define ansatz and parametrizations which contain warping factors, running constants (in time and extra dimension coordinates) and effective nonlinear gravitational polarizations. Such anisotropic vacuum toroidal metrics, the first example was given in gr-qc/0005025, differ substantially from the well known toroidal black holes (see hep-th/9511188 and gr-qc/9709013) which were constructed as non-vacuum solutions of the Einstein-Maxwell gravity with cosmological constant. Finally, we analyze two anisotropic 5D and 4D black tori solutions with cosmological constant.

J. Agresti, R. Pietri, L. Lusanna et al.

A Hamiltonian linearization of the rest-frame instant form of tetrad gravity (gr-qc/0302084), where the Hamiltonian is the weak ADM energy ${\hat E}_{ADM}$, in a completely fixed (non harmonic) 3-orthogonal Hamiltonian gauge is defined. For the first time this allows to find an explicit solution of all the Hamiltonian constraints and an associated linearized solution of Einstein's equations. It corresponds to background-independent gravitational waves in a well defined post-Minkowskian Christodoulou-Klainermann space-time.

G. Kirilin

There is a statement on the parametrization dependence of the classical metric in the recent paper of N.E.J. Bjerrum-Bohr, J.F. Donoghue, B.R. Holstein, gr-qc/0610096. I completely disagree with this statement. Here I show reparametrization invariance of the classical metric.