Date: Thu, 28 Apr 11 00:04:52 GMT Subject: gr-qc daily 6 new + 9 crosses received by eprepget ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ Send any comments regarding submissions directly to submitter. ------------------------------------------------------------------------------ Archives at http://arxiv.org/ To unsubscribe, e-mail To: gr-qc@arXiv.org, Subject: cancel ------------------------------------------------------------------------------ received by eprepget from Tue 26 Apr 11 20:00:00 GMT to Wed 27 Apr 11 20:00:00 GMT ------------------------------------------------------------------------------ \\ arXiv:1104.5058 Date: Wed, 27 Apr 2011 00:44:58 GMT (377kb) Title: Double-Kasner Spacetime: Peculiar Velocities and Cosmic Jets Authors: C. Chicone, B. Mashhoon and K. Rosquist Categories: gr-qc Comments: 37 pages, 5 figures \\ In dynamic spacetimes in which asymmetric gravitational collapse/expansion is taking place, the timelike geodesic equation appears to exhibit an interesting property: Relative to the collapsing configuration, free test particles undergo gravitational "acceleration" and form a double-jet configuration parallel to the axis of collapse. We illustrate this aspect of peculiar motion in simple spatially homogeneous cos- mological models such as the Kasner spacetime. To estimate the effect of spatial inhomogeneities on cosmic jets, timelike geodesics in the Ricci-flat double-Kasner spacetime are studied in detail. While spatial inhomogeneities can significantly modify the structure of cosmic jets, we find that under favorable conditions the double-jet pattern can initially persist over a finite period of time for sufficiently small inhomogeneities. \\ ( http://arxiv.org/abs/1104.5058 , 377kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5095 Date: Wed, 27 Apr 2011 09:21:06 GMT (15kb) Title: Poincare-Cartan form for scalar fields in curved background Authors: Pankaj Sharan Categories: gr-qc hep-th Comments: LaTeX2e, 18 pages \\ Poincare-Cartan form for scalar field is constructed as a differential 4-form in a `directly Hamiltonian' formalism which does not use a Lagrangian. The canonical momentum $p$ of a scalar field $\phi$ is a 1-form and the Poincare-Cartan 4-form $\Theta$ is $(*p)\ww d\phi-H$ where the Hamiltonian $H$ is a suitable 4-form made from $\phi$ and $p$ using the Hodge star operator defined by the Riemannian metric of the background spacetime. An allowed field configuration is a 4-dimensional surface in the 9-dimensional extended phase space such that its tangent vectors annihilate $\Omega=-d\Theta$. Relation of this to variational principle, symmetry fields and conserved quantities is worked out. Observables are defined as differential 4-forms constructed from field and momenta smeared with appropriate test functions. A bracket defined by Peierls long ago is found to be the suitable candidate for quantization. \\ ( http://arxiv.org/abs/1104.5095 , 15kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5108 Date: Wed, 27 Apr 2011 10:28:24 GMT (537kb,D) Title: Vacuum Solution of a Linear Red-Shift Based Correction in f(R) Gravity Authors: Solmaz Asgari and Reza Saffari Categories: gr-qc hep-th Comments: 6 pages, 7 figures \\ In this paper we have considered a red-shift based linear correction of derivative of action in context of f(R) gravity in vacuum. Here we have obtained that the linear correction may describe the late time acceleration which is appeared by SNeIa without need to dark energy and dark matter. Early time behavior of linear correction recovers radiation dominated era. Also we have calculated the asymptotic action for desired correction. The value of all solutions may reduce to de' Sitter universe in the absent of correction term. \\ ( http://arxiv.org/abs/1104.5108 , 537kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5116 Date: Wed, 27 Apr 2011 11:39:33 GMT (5kb) Title: Nonlinear spinor field in Bianchi type-II spacetime Authors: Bijan Saha Categories: gr-qc Comments: 5 pages \\ Within the scope of a Bianchi type-II (BII) cosmological model we study the role of a nonlinear spinor field in the evolution of the Universe. The system allows exact solutions only for some special choice of spinor field nonlinearity. \\ ( http://arxiv.org/abs/1104.5116 , 5kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5192 Date: Wed, 27 Apr 2011 17:09:17 GMT (6kb) Title: Orbital effects of spatial variations of fundamental coupling constants Authors: Lorenzo Iorio Categories: gr-qc astro-ph.EP physics.space-ph Comments: Latex2e, 9 pages, no figures, no tables. It is just a draft conveying the core results. It will be updated by including more material \\ We deal with the effects induced on the orbit of a test particle revolving around a central body by putative spatial variations of fundamental coupling constants $\zeta$. In particular, we assume a dipole gradient for $\zeta(\bds r)/\bar{\zeta}$ along a generic direction $\bds{\hat{k}}$ in space. We analytically work out the long-term variations of all the six standard Keplerian orbital elements parameterizing the orbit of a test particle in a gravitationally bound two-body system. It turns out that, apart from the semi-major axis $a$, the eccentricity $e$, the inclination $I$, the longitude of the ascending node $\Omega$, the longitude of pericenter $\pi$ and the mean anomaly $\mathcal{M}$ undergo non-zero long-term changes. By using the usual decomposition along the radial ($R$), transverse ($T$) and normal ($N$) directions, we also analytically work out the long-term changes $\Delta R,\Delta T,\Delta N$ and $\Delta v_R,\Delta v_T,\Delta v_N$ experienced by the position and the velocity vectors $\bds r$ and $\bds v$ of the test particle. It turns out that, apart from $\Delta N$, all the other five shifts do not vanish over one full orbital revolution. In the calculation we do not use \textit{a-priori} simplifying assumptions concerning $e$ and $I$. Thus, our results are valid for a generic orbital geometry; moreover, they hold for any gradient direction. \\ ( http://arxiv.org/abs/1104.5192 , 6kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5205 Date: Wed, 27 Apr 2011 18:11:24 GMT (5kb) Title: A Note on the Coordinate Freedom in Describing the Motion of Particles in General Relativity Authors: Samuel E. Gralla and Robert M. Wald Categories: gr-qc \\ Our previous work developed a framework for treating the motion of a small body in general relativity, based on a one-parameter-family of solutions to Einstein's equation. Here we give an analysis of the coordinate freedom allowed within this framework, as is needed to determine the form of the equations of motion when they are expressed in general gauges. \\ ( http://arxiv.org/abs/1104.5205 , 5kb) %-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%- ------------------------------------------------------------------------------ \\ arXiv:1104.3796 (*cross-listing*) Date: Tue, 19 Apr 2011 16:34:12 GMT (29kb,D) Title: Persistence of black holes through a cosmological bounce Authors: B. J. Carr and A.A. Coley Categories: astro-ph.CO gr-qc Comments: 8 pages, 1 figure \\ We discuss whether black holes could persist in a universe which recollapses and then bounces into a new expansion phase. Whether the bounce is of classical or quantum gravitational origin, such cosmological models are of great current interest. In particular, we investigate the mass range in which black holes might survive a bounce and ways of differentiating observationally between black holes formed just after and just before the last bounce. We also discuss the consequences of the universe going through a sequence of dimensional changes as it passes through a bounce. \\ ( http://arxiv.org/abs/1104.3796 , 29kb) ------------------------------------------------------------------------------ \\ arXiv:1104.4907 (*cross-listing*) Date: Tue, 26 Apr 2011 12:55:23 GMT (668kb) Title: Probing AdS Wormholes by Entanglement Entropy Authors: Mitsutoshi Fujita, Yasuyuki Hatsuda, Tadashi Takayanagi Categories: hep-th gr-qc Comments: 17 pages, 6 figures \\ In this paper, we study the Lorentzian AdS wormhole solutions constructed in arXiv:0808.2481 [hep-th]. Each of them is a classical solution interpolating between an AdS space and a flat space in type IIB supergravity. We calculate the holographic entanglement entropy to probe this geometry. Our analysis shows that there exits a mass gap in its holographic dual gauge theory and that the entanglement between the two boundaries is rather suppressed than that we naively expect for wormholes. We also examine the holographic conductivity on a probe D-brane in this spacetime. \\ ( http://arxiv.org/abs/1104.4907 , 668kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5027 (*cross-listing*) Date: Tue, 26 Apr 2011 20:12:31 GMT (60kb) Title: The Mass and Radius of the Neutron Star in the Bulge Low-Mass X-ray Binary KS 1731-260 Authors: Feryal Ozel, Andrew Gould, and Tolga Guver Categories: astro-ph.GA gr-qc nucl-th Comments: submitted to ApJ \\ Measurements of neutron star masses and radii are instrumental for determining the equation of state of their interiors, understanding the dividing line between neutron stars and black holes, and for obtaining accurate statistics of source populations in the Galaxy. We report here on the measurement of the mass and radius of the neutron star in the low-mass X-ray binary KS 1731-260. The analysis of the spectroscopic data on multiple thermonuclear bursts yields well-constrained values for the apparent angular area and the Eddington flux of the source, both of which depend in a distinct way on the mass and radius of the neutron star. The binary KS 1731-260 is in the direction of the Galactic bulge, allowing a distance estimate based on the density of stars in that direction. Making use of the Han & Gould model, we determine the probability distribution over the distance to the source, which is peaked at 8 kpc. Combining these measurements, we place a strong upper bound on the radius of the neutron star, R <= 12 km, while confining its mass to M <= 1.8 M_sun. \\ ( http://arxiv.org/abs/1104.5027 , 60kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5049 (*cross-listing*) Date: Tue, 26 Apr 2011 23:20:36 GMT (556kb) Title: Dark energy, co-evolution of massive black holes with galaxies, and ASTROD-GW Authors: Wei-Tou Ni Categories: astro-ph.CO gr-qc hep-ph Comments: 16 pages,5 figures, Paper (COSPAR paper number H05-0017-10) presented in the 38th COSPAR Scientific Assembly, 18-25 July 2010, Bremen, Germany (2010), submitted to Advances in Space Research \\ The detection of low frequency band (100 nHz-100 mHz) and very low frequency band (300 pHz-100 nHz) gravitational waves (GWs) is important for exploration of the equation of state of dark energy and the co-evolution of massive black holes (MBHs) with galaxies. Most galaxies are believed to have a massive black hole in the galactic core. In the formation of these black holes, merging and accretion are the two main processes. Merging of massive black holes generate GWs which could be detected by space GW detectors and pulsar timing arrays (PTAs) to cosmological distances. LISA (Laser-Interferometric Space Antenna) is most sensitive to the frequency band 1 mHz-100 mHz, ASTROD-GW (ASTROD [Astrodynamical Space Test of Relativity using Optical Devices] optimized for Gravitation Wave detection) is most sensitive to the frequency band 100 nHz-1 mHz and PTAs are most sensitive to the frequency band 300 pHz-100 nHz. In this paper, we discuss the sensitivities and outlooks of detection of GWs from binary massive black holes in these frequency bands with an emphasis on ASTROD-GW. The GWs generated by the inspirals, merging and subsequent ringdowns of binary black holes are standard sirens to the cosmological distance. Using GW observations, we discuss the methods for determining the equation of state of dark energy and for testing the co-evolution models of massive black holes. The scientific aim of ASTROD-GW is focused for gravitational wave detection at low frequency. The science goals include detection of GWs from MBHs, and Extreme-Mass-Ratio Black Hole Inspirals (EMRI), and using these observations to find the evolution of the equation of state of dark energy and to explore the co-evolution of massive black holes with galaxies. \\ ( http://arxiv.org/abs/1104.5049 , 556kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5072 (*cross-listing*) Date: Wed, 27 Apr 2011 04:17:40 GMT (35kb,D) Title: Electrovacuum Near-horizon Geometries in Four and Five Dimensions Authors: Hari K. Kunduri Categories: hep-th gr-qc Comments: Invited contribution to a special issue of Classical and Quantum Gravity on the 19th International Conference on General Relativity and Gravitation, Mexico City, July 5-9, 2010 Report-no: Alberta-THY-07-11 \\ Associated to every stationary extremal black hole is a unique near-horizon geometry, itself a solution of the field equations. These latter spacetimes are more tractable to analyze and most importantly, retain properties of the original black hole which are intrinsic to the event horizon. After reviewing general features of near-horizon geometries, such as SO(2,1) symmetry enhancement, I report on recent work on stationary, charged extremal black hole solutions of the Einstein-Maxwell equations with a negative cosmological constant in four dimensions and present a classification of near-horizon geometries of black holes on this kind. In five dimensions, charged extremal black hole solutions to minimal (gauged) supergravity, which arises naturally in string theory and the gauge theory/gravity correspondence, are considered. I consider the classification of near-horizon geometries for the subset of such black holes which are supersymmetric. Recent progress on the classification problem in the general extremal, non-supersymmetric case is also discussed. \\ ( http://arxiv.org/abs/1104.5072 , 35kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5142 (*cross-listing*) Date: Wed, 27 Apr 2011 13:50:56 GMT (13kb) Title: Gravity/CFT correspondence for three dimensional Einstein gravity with a conformal scalar field Authors: M. Hasanpour, F. Loran, H. Razaghian Categories: hep-th gr-qc Comments: 16 pages \\ We study the three dimensional Einstein gravity conformally coupled to a scalar field. Solutions of this theory are geometries with vanishing scalar curvature. We consider solutions with a constant scalar field which corresponds to an infinite Newton's constant. There is a class of solutions with possible curvature singularities which asymptotic symmetries are given by two copies of the Virasoro algebra. We argue that the central charge of the corresponding CFT is infinite. Furthermore, we construct a family of Schwarzschild solutions which can be conformally mapped to the Martinez-Zanelli solution of Einstein's equations with a negative cosmological constant coupled to conformal scalar field. \\ ( http://arxiv.org/abs/1104.5142 , 13kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5158 (*cross-listing*) Date: Wed, 27 Apr 2011 14:56:51 GMT (438kb) Title: Bounding bubbles: the vertex representation of 3d Group Field Theory and the suppression of pseudo-manifolds Authors: Sylvain Carrozza, Daniele Oriti Categories: hep-th gr-qc Comments: 28 pages, 17 figures \\ Based on recent work on simplicial diffeomorphisms in colored group field theories, we develop a representation of the colored Boulatov model, in which the GFT fields depend on variables associated to vertices of the associated simplicial complex, as opposed to edges. On top of simplifying the action of diffeomorphisms, the main advantage of this representation is that the GFT Feynman graphs have a different stranded structure, which allows a direct identification of subgraphs associated to bubbles, and their evaluation is simplified drastically. As a first important application of this formulation, we derive new scaling bounds for the regularized amplitudes, organized in terms of the genera of the bubbles, and show how the pseudo-manifolds configurations appearing in the perturbative expansion are suppressed as compared to manifolds. Moreover, these bounds are proved to be optimal. \\ ( http://arxiv.org/abs/1104.5158 , 438kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5163 (*cross-listing*) Date: Wed, 27 Apr 2011 15:32:49 GMT (887kb,D) Title: Recent results from VHE gamma astrophysics related to fundamental physics and cosmic rays Authors: Alessandro De Angelis Categories: astro-ph.HE gr-qc hep-ex hep-ph Comments: Invited talk at ECRS 2010, Turku \\ High-energy photons are a powerful probe for astrophysics and for fundamental physics under extreme conditions. During the recent years, our knowledge of the most violent phenomena in the universe has impressively progressed thanks to the advent of new detectors for very-high-energy (VHE) gamma rays (above 100 GeV). Ground-based detectors like the Cherenkov telescopes (H.E.S.S., MAGIC and VERITAS) recently discovered more than 80 new sources. This talk reviews the present status of VHE gamma astrophysics, with emphasis on the recent results and on the experimental developments, keeping an eye on the future. The impact on fundamental physics and on cosmic-ray physics is emphasized. \\ ( http://arxiv.org/abs/1104.5163 , 887kb) ------------------------------------------------------------------------------ \\ arXiv:1104.5215 (*cross-listing*) Date: Wed, 27 Apr 2011 18:59:35 GMT (87kb) Title: 3D black holes on a 2-brane in 4D Minkowski space Authors: D. Bazeia, F. A. Brito and F. G. Costa Categories: hep-th gr-qc Comments: 9 pages, 4 figures, Latex \\ We investigate three-dimensional black hole solutions in the realm of pure and new massive gravity in 2+1 dimensions induced on a 2-brane embedded in a flat four-dimensional spacetime. There is no cosmological constant neither on the brane nor on the four-dimensional bulk. Only gravitational fields are turned on and we indeed find vacuum solutions as black holes in 2+1 dimensions even in the absence of any cosmological solution. There is a crossover scale that controls how far the three- or four-dimensional gravity manifests on the 2-brane. Our solutions also indicate that local BTZ solutions can flow to local four-dimensional Schwarzschild like black holes, as one probes from small to large distances, which is clearly a higher dimensional manifestation on the 2-brane. This is similar to the DGP scenario where the effects of extra dimensions for large probed distances along the brane manifest. \\ ( http://arxiv.org/abs/1104.5215 , 87kb) %%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%% ------------------------------------------------------------------------------ \\ arXiv:1008.1763 (*cross-listing*) replaced with revised version Wed, 27 Apr 2011 11:19:32 GMT (27kb) Title: Generalized Geometry and M theory Authors: David S. Berman and Malcolm J. Perry Categories: hep-th gr-qc Comments: 29 pages of Latex, v2 References added, typos fixed, v3 corrected kinetic term and references added Report-no: QMUL-PH-10-10 \\ ( http://arxiv.org/abs/1008.1763 , 27kb) ------------------------------------------------------------------------------ \\ arXiv:1102.5423 replaced with revised version Wed, 27 Apr 2011 14:07:29 GMT (390kb) Title: Time Domain Simulations of Arm Locking in LISA Authors: James Ira Thorpe, Peiman Maghami, Jeffrey Livas Categories: gr-qc astro-ph.IM Comments: Revised to address reviewer comments. Accepted by Phys. Rev. D \\ ( http://arxiv.org/abs/1102.5423 , 390kb) ------------------------------------------------------------------------------ \\ arXiv:1103.4215 (*cross-listing*) replaced with revised version Wed, 27 Apr 2011 16:37:41 GMT (5231kb) Title: Testing feasibility of scalar-tensor gravity by scale dependent mass and coupling to matter Authors: D. F. Mota, V. Salzano, S. Capozziello Categories: astro-ph.CO gr-qc hep-th Comments: 30 pages, 15 figures, to appear in Phys. Rev. D \\ ( http://arxiv.org/abs/1103.4215 , 5231kb) %%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%--- For subscribe options to combined physics archives, e-mail To: physics@arXiv.org, Subject: subscribe ----------------------------------------------------------------------------- For help on viewing and making submissions, see http://arXiv.org/help/ For a list of archive mirror sites, see http://arXiv.org/servers.html ----------------------------------------------------------------------------- Third-party submissions cause excessive problems. Author self-submissions are exceedingly preferred. E-mail submissions have been discontinued in favor of better support for Web submissions. See http://arXiv.org/help/uploads