Hasil untuk "gr-qc"

Cristhian Garcia-Quintero, Mustapha Ishak, Logan Fox et al.

We introduce a new version of the Integrated Software in Testing General Relativity (ISiTGR) which is a patch to the software CAMB and CosmoMC. ISiTGR is intended to test deviations from GR at cosmological scales using cosmological data sets. While doing so, it allows for various extensions to the standard flat $Λ$CDM model. In this new release, we have support for the following: 1) dynamical dark energy parametrizations with a constant or time-dependent equation of state; 2) a consistent implementation of anisotropic shear to model massive neutrinos throughout the full formalism; 3) multiple commonly-used parametrizations of modified growth (MG) parameters; 4) functional, binned and hybrid time- and scale-dependencies for all MG parameters; 5) spatially flat or curved backgrounds. ISiTGR is designed to allow cosmological analyses to take full advantage of ongoing and future surveys to test simultaneously or separately various extensions to the standard model. We describe here the formalism and its implementation in the CMB code, the Integrated Sachs-Wolfe (ISW) effect, and the 3x2 point statistics. Next, we apply ISiTGR to current data sets from Planck-2018, Planck-2015, Dark Energy Survey YR1 release, Baryonic Acoustic Oscillations (BAO), Redshift Space Distortions (BAO/RSD) from the BOSS Data Release 12, the 6DF Galaxy Survey and the SDSS Data Release 7 Main Galaxy Sample, and Supernova from the Pantheon compilation, joint SNLS/SDSS data analysis and the Hubble Space Telescope. We derive constraints on MG parameters for various combinations of the five features above and find that GR is consistent with current data sets in all cases. The code is made publicly available at \url{https://github.com/mishakb/ISiTGR}.

Inyong Cho

We briefly introduce the inflation model driven by a massive scalar field in Eddington-inspired Born-Infeld gravity [1] investigated in [2]. We present the recent results of the tensor perturbation in this model investigated in [3]. For short wave-length modes, the perturbation feature is very similar to that of the usual chaotic inflation. For long wave-length modes, the perturbation exhibits a peculiar rise in the power spectrum which may leave a signature in the cosmic microwave background radiation. We also briefly discuss the scalar perturbation in this model. References [1] M. Banados and P. G. Ferreira, Eddington’s theory of gravity and its progeny, Phys. Rev. Lett. 105, 011101 (2010) [arXiv:1006.1769 [astro-ph.CO]]. [2] I. Cho, H.-C. Kim and T. Moon, Precursor of Inflation, Phys. Rev. Lett 111, 071301 (2013) [arXiv:1305.2020 [gr-qc]]. [3] I. Cho and H.-C. Kim, Inflationary Tensor Perturbation in Eddington-inspired Born-Infeld gravity, arXiv:1404.6081 [gr-qc].

P. Boonserm, Napasorn Jongjittanon, T. Ngampitipan

Philipp A. Hoehn

A canonical quantum formalism for discrete systems subject to a discretization changing dynamics is outlined. This framework enables one to systematically study (non-)unitarity of such dynamics, the role of canonical constraints and the fate of Dirac observables on temporally varying discretizations. It will be illustrated how the formalism can also be employed to generate a vacuum for a scalar field on an evolving lattice. Implications for the dynamics in simplicial quantum gravity models are commented on. References [1] P. A. Höhn, “Quantization of systems with temporally varying discretization I: Evolving Hilbert spaces” arXiv:1401.6062 [gr-qc]. [2] P. A. Höhn, “Quantization of systems with temporally varying discretization II: Local evolution moves” arXiv:1401.7731 [gr-qc]. [3] B. Dittrich and P. A. Höhn, “Constraint analysis for variational discrete systems” J.Math. Phys.54, 093505 (2013) [arXiv:1303.4294 [math-ph]]. [4] B. Dittrich, P. A. Höhn and T. Jacobson, to appear

J. Świeżewski

I will present a construction of observables following naturally from an introduction of an observer into a relativistic theory. The observables are invariant under a large class of spatial diffeomorphisms. I will discuss the description of the theory in terms of spatial-diffeomorphisminvariant degrees of freedom. The talk will be based on [1]. References [1] P. Duch, W. Kaminski, J. Lewandowski and J. Swieżewski, Observables for General Relativity related to geometry, arXiv:1403.8062 [gr-qc].

E. Livine

The spinfoam framework defines transition amplitudes for spin network states of loop quantum gravity. I will review their recent reformulation in terms of spinorial variables allowing to see these amplitudes as coherent state path integrals [1,2,3]. This clarifies their geometrical meaning and at the identification of symmetries: recursion relations for 3nj symbols are turned into Hamiltonian constraints satisfied by the spinfoam amplitudes [4,5]. This applies in particular to the derivation of modified FRW equations for quantum cosmology [6]. References [1] L Freidel and S Speziale, From twistors to twisted geometries, Phys. Rev. D 82, 084041 (2010) arXiv:1006.0199 [gr-qc] [2] E F Borja, L Freidel, I Garay and E R Livine, U(N) tools for Loop Quantum Gravity: The Return of the Spinor, Class. Quant. Grav. 28, 055005 (2011) arXiv:1010.5451 [gr-qc] [3] M Dupuis and E R Livine, Holomorphic Simplicity Constraints for 4d Riemannian Spinfoam Models, J. Phys. Conf. Ser. 360, 012046 (2012) arXiv:1111.1125 [gr-qc] [4] V Bonzom, E R Livine and S Speziale, Recurrence relations for spin foam vertices, Class. Quant. Grav. 27, 125002 (2010) arXiv:0911.2204 [gr-qc] [5] V Bonzom and E R Livine, Generating Functions for Coherent Intertwiners, Class. Quant. Grav. 30, 055018 (2013) arXiv:1205.5677 [gr-qc] [6] E R Livine and M Martin-Benito, Classical Setting and Effective Dynamics for Spinfoam Cosmology, Class. Quant. Grav. 30, 035006 (2013) arXiv:1111.2867 [gr-qc]

Ming-Shu Chen, Chen-Mao Liao, Ming-Hsun Wu et al.

M. Azreg-Aïnou

We briefly discuss some of the known and new properties of rotating geometries that are relevant to this work. We generalize the analytical method of superposition of fields, known for generating nonrotating solutions, and apply it to construct massless and massive rotating physical wormholes sourced by a source-free electromagnetic field and an exotic fluid both anisotropic. Their stress-energy tensors are presented in compact and general forms. For the massive rotating wormholes there exists a mass–charge constraint yielding almost no more dragging effects than ordinary stars. There are conical spirals through the throat along which no local negative energy densities are noticed for these rotating wormholes. This conclusion extends to nonrotating massive type I wormholes derived previously by the author, which seem to be the first kind of nonrotating wormholes with this property. Based on the classification made in Azreg-Aïnou (J Cosmol Astropart Phys 07:037, arXiv:1412.8282 [gr-qc], 2015): “Type I wormholes have their radial pressure dying out faster, as one moves away from the throat, than any other component of the stress-energy and thus violate the least the local energy conditions. In type II (resp. III) the radial and transverse pressures are asymptotically proportional and die out faster (resp. slower) than the energy density”.

V. O. Thomas, D. M. Pandya

In this paper a new class of exact solutions of Einstein’s field equations for compact stars with charged distributions is obtained on the basis of pseudo-spheroidal spacetime characterized by the metric potential grr=1+Kr2R21+r2R2$g_{rr}=\frac{1+K\frac{r^{2}}{R^{2}}}{1+\frac{r^{2}}{R^{2}}}$, where K$K$ and R$R$ are geometric parameters of the spacetime. The expressions for radial pressure (pr$p_{r}$) and electric field intensity (E$E$) are chosen in such a way that the model falls in the category of physically acceptable one. The bounds of geometric parameter K$K$ and the physical parameters p0$p_{0}$ and α$\alpha$ are obtained by imposing the physical requirements and regularity conditions. The present model is in good agreement with the observational data of various compact stars like 4U 1820-30, PSR J1903+327, 4U 1608-52, Vela X-1, SMC X-4, Cen X-3 given by Gangopadhyay et al. (Mon. Not. R. Astron. Soc. 431:3216, 2013). When α=0$\alpha = 0$, the model reduces to the uncharged anisotropic distribution given by Thomas and Pandya (arXiv:1506.08698v1 [gr-qc], 2015).

J. Kluson

This short note is devoted to the Hamiltonian formulation of the conformal decomposition of the gravitational field that was performed in [gr-qc/0501092]. We also analyze the gauge fixed form of the theory when we fix the conformal symmetry by imposing the condition det g=1.

SangChul Yoon

We work on the uniqueness, gr-qc/0504147, of representations of the holonomy-flux algebra in loop quantum gravity. We argue that for analytic diffeomorphisms, the flux operators can be only constants as functions on the configuration space in representations with no anomaly, which are zero in the standard representation.

Rafael A. Porto, I. Rothstein

In this comment we explain the discrepancy found between the results in arXiv:0712.1716v1 for the 3PN spin-spin potential and those previously derived in gr-qc/0604099. We point out that to compare one must include sub-leading lower order spin-orbit effects which contribute to the spin-spin potential once one transforms to the PN frame. When these effects are included the results in arXiv:0712.1716v1 do indeed reproduce those found in gr-qc/0604099.

Can Aktas, Ihsan Yilmaz

This paper has been removed by arXiv administrators because it plagiarizes astro-ph/0611537, astro-ph/0506256, astro-ph/0203033, astro-ph/0311128, gr-qc/0505144, astro-ph/0611460, and astro-ph/0610840.

Kayll Lake

Recently, Helliwell and Konkowski (\texttt{gr-qc/0701149}) have examined the quantum "healing" of some classical singularities in certain power-law spacetimes. Here I further examine classical properties of these spacetimes and show that some of them contain naked strong curvature singularities.

N. Yunes, Wolfgang Tichy Penn State University, Florida Atlantic University

We construct approximate initial data for nonspinning black hole binary systems by asymptotically matching the 4-metrics of two tidally perturbed Schwarzschild solutions in isotropic coordinates to a resummed post-Newtonian 4-metric in ADMTT coordinates. The specific matching procedure used here closely follows the calculation in [N. Yunes, W. Tichy, B. J. Owen, and B. Bruegmann, gr-qc/0503011.], and is performed in the so-called buffer zone where both the post-Newtonian and the perturbed Schwarzschild approximations hold. The result is that both metrics agree in the buffer zone, up to the errors in the approximations. However, since isotropic coordinates are very similar to ADMTT coordinates, matching yields better results than in the previous calculation [N. Yunes, W. Tichy, B. J. Owen, and B. Bruegmann, gr-qc/0503011.], where harmonic coordinates were used for the post-Newtonian 4-metric. In particular, not only does matching improve in the buffer zone, but due to the similarity between ADMTT and isotropic coordinates the two metrics are also close to each other near the black hole horizons. With the help of a transition function we also obtain a global smooth 4-metric which has errors on the order of the error introduced by the more accurate of the two approximations we match. Thismore » global smoothed out 4-metric is obtained in ADMTT coordinates which are not horizon penetrating. In addition, we construct a further coordinate transformation that takes the 4-metric from global ADMTT coordinates to new coordinates which are similar to Kerr-Schild coordinates near each black hole, but which remain ADMTT further away from the black holes. These new coordinates are horizon penetrating and lead, for example, to a lapse which is everywhere positive on the t=0 slice. Such coordinates may be more useful in numerical simulations.« less

H. Khosravi, M. Naseri, S. Rouhani et al.

An explicit calculation of Casimir effect through an alternative approach of field quantization [J.P. Gazeau, J. Renaud, M.V. Takook, Class. Quantum. Grav. 17 (2000) 1415, gr-qc/9904023; M.V. Takook, Int. J. Mod. Phys. E 11 (2002) 509, gr-qc/0006019], has been presented in this Letter. In this method, the auxiliary negative norm states have been utilized, the modes of which do not interact with the physical states or real physical world. Naturally these modes cannot be affected by the physical boundary conditions. Presence of negative norm states play the role of an automatic renormalization device for the theory.

Adel M Awad

O. Aydoğdu, M. Salti, M. Korunur

This paper has been removed by arXiv administrators because it overlaps gr-qc/0303009, hep-th/0405047, gr-qc/0412120, and others. This paper also has excessive overlap with the following papers also written by the authors or their collaborators: gr-qc/0607119, gr-qc/0607103, gr-qc/0607115, and others.

G. Amelino-Camelia, D. Benedetti, F. D’Andrea et al.

We consider the two most studied proposals of relativity theories with observer-independent scales of both velocity and length/mass: the one discussed by Amelino-Camelia as an illustrative example for the original proposal (Preprint gr-qc/0012051) of theories with two relativistic invariants, and an alternative more recently proposed by Magueijo and Smolin (Preprint hep-th/0112090). We show that these two relativistic theories are much more closely connected than it would appear on the basis of a naive analysis of their original formulations. In particular, in spite of adopting a rather different formal description of the deformed boost generators, they end up assigning the same dependence of momentum on rapidity, which can be described as the core feature of these relativistic theories. We show that this observation can be used to clarify the concepts of particle mass, particle velocity and energy–momentum conservation rules in these theories with two relativistic invariants.

P. Zizzi

In a previous paper (gr-qc/9907063) we described the early inflationary universe in terms of quantum information. In this paper, we analize those results in more detail, and we stress the fact that during inflation, the universe can be described as a superposed state of quantum registers. The self-reduction of the superposed quantum state is consistent with the Penrose's Objective Reduction (OR) model. The quantum gravity threshold is reached at the end of inflation, and corresponds to a superposed state of 109 quantum registers. This is also the number of superposed tubulins-qubits in our brain, which undergo the Penrose-Hameroff's Orchestrated Objective Reduction, (Orch OR), leading to a conscious event. Then, an analogy naturally arises between the very early quantum computing universe, and our mind.