Hasil untuk "gr-qc"

Gregory Jarequi, Soumodeep Mitra, Varun Vaidya

We apply the point particle EFT approach to a compact star to systematically compute dynamical tidal love numbers for various non-rotating compact objects, extending the treatment of {arXiv:2307.10391[hep-th], arXiv:2407.08327 [gr-qc]}. We calculate the scattering amplitude in Black Hole Perturbation Theory(BPHT) for \textit{arbitrary} non-rotating compact stars using the Mano-Suzuki-Takasugi(MST) method with non zero surface reflectivity and match it with that obtained from point particle EFT order by order in the low frequency expansion. This sets up a systematic framework for extracting the static and dynamical tidal love numbers(TLNs) to any order in the multipole expansion. In this paper, we employ the technique to compute the Next-to-Next-to Leading Order TLN upto a universal constant and its Renormalization Group equation for non-viscous Neutron stars and Neutron stars admixed with Bosonic or Fermionic dark matter.

Francisco S. N. Lobo

In this work, we employ the Darmois-Israel thin-shell formalism to construct both static and dynamic thin-shell configurations surrounding traversable wormholes. Initially, using the cut-and-paste technique, we perform a linearized stability analysis in the presence of a general cosmological constant. Our results show that for sufficiently large positive values of the cosmological constant, corresponding to the Schwarzschild-de Sitter geometry, the stability regions of the wormhole solutions are significantly enhanced compared to the Schwarzschild case. Subsequently, we construct static thin-shell solutions by matching an interior wormhole geometry to an exterior vacuum spacetime across a junction surface. In the spirit of minimizing the presence of exotic matter, we identify parameter domains in which the null and weak energy conditions are satisfied at the shell. We examine the surface stress-energy components in detail, determining regions where the tangential surface pressure is either positive or negative, interpreted, respectively, as the pressure or surface tension. Additionally, an expression describing the behavior of the radial pressure across the junction is derived. Finally, we determine key geometrical characteristics of the wormhole, including the throat radius and the junction interface radius, by imposing traversability conditions. Estimates for the traversal time and required velocity are also provided, further elucidating the physical viability of these configurations.

T. Padmanabhan

It is possible to provide a physical interpretation for the field equations of gravity based on a thermodynamical perspective. The virtual degrees of freedom associated with the horizons perceived by the local Rindler observers, play a crucial role in this approach. In this context, the relation S=E/2T between the entropy (S), active gravitational mass (E) and temperature (T) - obtained previously in gr-qc/0308070 [CQG, 21, 4485 (2004)] - can be reinterpreted as the law of equipartition E = (1/2) nkT where n=A/L_P^2 is the number (density) of microscopic horizon degrees of freedom. Conversely, one can use the equipartition argument to provide a thermodynamic interpretation of even non-relativistic gravity. These results emphasize the intrinsic quantum nature of all gravitational phenomena and diminishes the distinction between thermal phenomena associated with local Rindler horizons and the usual thermodynamics of macroscopic bodies in non-inertial frames. Just like the original thermodynamic interpretation, these results also hold for a wide class of gravitational theories like the Lanczos-Lovelock models.

Richard A. Brown

In this thesis we investigate certain cosmological brane world models of the Randall-Sundrum type. The models are motivated by string theory but we focus on the phenomenology of the cosmology. Two models of specific interest are the Dvali-Gabadadze-Porrati (DGP, induced-gravity) model, where the brane action is modified, and the Gauss-Bonnet model where the bulk action is modified. Both of these modifications maybe motivated by string theory. We provide a brief review of Randall-Sundrum models and then consider the Kaluza-Klein modes on Minkowski and de Sitter branes, in both the two and one brane cases. The spectrum obtained for the de Sitter branes is a new result. We then consider a Friedmann-Robertson-Walker brane in order to investigate the cosmological dynamics on the brane. We present a brief discussion of the DGP and Gauss-Bonnet brane worlds. We then investigate the Gauss-Bonnet-Induced-Gravity (GBIG) model where the Gauss-Bonnet (GB) bulk term is combined with the induced-gravity (IG) brane term of the DGP model. We present a thorough investigation of cosmological dynamics, in particular focusing on GBIG models that behave like self-accelerating DGP models at late times but at early times show the remarkable feature of a finite-temperature Big Bang. We also discuss the constraints from observations, including ages and Big Bang nucleosynthesis.

F. Smith

This paper discusses the Higgs and spinor fermion terms of the D4-D5-E6 model of a series of papers (hep-ph/9301210, hep-th/9302030, hep-th/9306011, and hep-th/9402003) an 8-dimensional spacetime is reduced to 4-dimensions. The gauge boson terms give SU(3)xSU(2)xU(1) for the color, weak, and electromagnetic forces and gravity of the MacDowell-Mansouri type, which has recently been shown by Nieto, Obregon, and Socorro (gr-qc/9402029) to be equivalent, up to a Pontrjagin topological term, to the Ashtekar formulation.

Johan Noldus, P. Esch

Abstract Hossenfelder proposes in [S. Hossenfelder, Phys. Lett. B 636 (2006) 119] and [S. Hossenfelder, gr-qc/0605083 ] a symmetry between gravitating and anti-gravitating particles by superposing a negative charge to classical relativity. This Letter explicitly shows that the latter proposal does not address any of the difficulties that arise in such context. On the contrary, the “world-lines” of the anti-gravitating particles are defined as observer-dependent entities and no attempt whatsoever to dynamically restore local boost invariance is made. Both papers simply focus on the erroneous construction of a new bundle attached to a preferred timelike vector field, although the author gives the impression that no such preference is needed.

I. Smolyaninov

Recently introduced toy surface plasmon "black holes" and "wormholes" (New Journal of Physics 5, 147.1-147.8 (2003), and gr-qc/0306089) can be used to create a toy "time machine" according to a number of published designs (see for example I.D. Novikov, Sov.Phys.JETP 68, 439 (1989)). Assuming that such a toy "time machine" does not work, a general prediction can be made of strong electromagnetic field enhancement inside an arbitrarily-shaped nanohole near an arising effective event horizon, which is supposed to prevent the toy "time machine" from being operational. This general result is useful in description of the nonlinear optical behavior of random nanoholes in metal films.

F. Binbay, I. Acikgoz, M. Salti

This paper has been removed by arXiv administrators because it plagiarizes gr-qc/9803014, "A White Hole Model of the Big Bang," by Philip Gibbs.

Toshifumi Sakaguchi

The paper entitled ``Against Many-Worlds Interpretations'' by A. Kent, which has recently been submitted to the e-Print archive (gr-qc/9703089) contained some misconceptions. The claims on Everett's many-worlds interpretation are quoted and answered.

F. Aquino

In a previous work it was shown that the gravitational and inertial masses are correlated by an adimensional factor, which depends on the incident radiation upon the particle. It was also shown that there is a direct correlation between the radiation absorbed by the particle and its gravitational mass, independently of the inertial mass. This finding has fundamental consequences to Unified Field Theory and Quantum Cosmology. Only in the absence of electromagnetic radiation the mentioned factor becomes equal to one. On the other hand, in specific electromagnetic conditions, it can be reduced, nullified or made negative. This means that there is the possibility of the gravitational masses can be reduced, nullified and made negative by means of electromagnetic radiation. This unexpected theoretical result was recently confirmed by an experiment (gr-qc/0005107). A fundamental consequence of the mentioned correlation is that , in specific ultra-high energy conditions, the gravitational and electromagnetic fields can be described by the same Hamiltonian , i.e., in these circumstances, they are unified. Such conditions can have occurred inclusive in the Initial Universe , before the first spontaneous breaking of symmetry. Taking as base this discovery, and starting from the gravitational mass of superparticles from the Initial Universe we show here that it is possible to deduce the reciprocal fine structure constant and the uncertainty principle directly from the Gravitation Theory(Unified Theory).

S. Rouhani, M. V. Takook

F. Henry-Couannier

The previous version of this article gave erroneous predictions. The correct uptodate predictions can be found in the section devoted to gravitomagnetism in the living review of the Dark Gravity theory: gr-qc/0610079 The most natural prediction is zero frame dragging and the same geodetic effect as predicted by GR. However, a straightforward extension of the theory could lead to the same frame-dragging as in GR.

S. Aygun, I. Tarhan, H. Baysal et al.

This paper has been removed by arXiv administrators because it plagiarizes gr-qc/0603075, 0706.3245, gr-qc/0403097, gr-qc/0404108, gr-qc/0303034, hep-th/0206052, and others. This paper has excessive overlap with the following papers also written by the authors or their collaborators: 0704.0525 and others.

D. Brill

This is a reply, given at the conference ``Mach's Principle" in T\"ubingen in July 1993, to the paper by Pfister (1993). Unfortunately the Pfister paper itself was not sent to gr-qc.

D. Brill

This is the reply given at the conference ``Mach's Principle" at T\"ubingen in July 1993 to the paper by Isenberg (1993a). Unfortunately the Isenberg paper itself was not submitted to gr-qc.

L. Susskind

In a recent paper on wormholes (gr-qc/0503097), the author of that paper demonstrated that he didn't know what he was talking about. In this paper I correct the author's naive erroneous misconceptions.

S. Aygun, M. Aygun, I. Tarhan

This paper has excessive overlap with the following papers also written by the authors or their collaborators: gr-qc/0607110, gr-qc/0607115, gr-qc/0607119, gr-qc/0607109, gr-qc/0607103, gr-qc/0607089, gr-qc/0602012, gr-qc/0608024, and others.

L. Pachon, J. Rueda

We dispose of some objections raised by Manko et al. (gr-qc/0604091) on a recently published paper on the role of Poynting vector in the ocurrence of vorticity in electrovaccum spacetimes (2006, Class. Quantum Grav. 23, 2395)

S. Aygun, M. Aygun, I. Tarhan

This paper has been removed by arXiv administrators because it plagiarizes gr-qc/0303009, hep-th/0405047, gr-qc/0602107, hep-th/0311050, and others. This paper has excessive overlap with the following papers also written by the authors or their collaborators: gr-qc/0607115, gr-qc/0607103, gr-qc/0606080, gr-qc/0607126, gr-qc/0607102, gr-qc/0510123, gr-qc/0607110, and others.

Giovanni Amelino-Camelia, Dario Benedetti, Francesco D'Andrea et al.