Date: Thu, 25 Dec 08 01:00:23 GMT Subject: gr-qc daily 3 new + 5 crosses received by eprepget ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ Send any complaints regarding submissions directly to submitter. ------------------------------------------------------------------------------ Point your www client at http://arXiv.org/ To unsubscribe, e-mail To: gr-qc@arXiv.org, Subject: cancel ------------------------------------------------------------------------------ received by eprepget from Tue 23 Dec 08 21:00:01 GMT to Wed 24 Dec 08 21:00:01 GMT ------------------------------------------------------------------------------ \\ arXiv:0812.4489 Date: Wed, 24 Dec 2008 10:10:07 GMT (247kb) Title: Relaxing the Cosmological Constraints on Unparticle Dark Component Authors: Hao Wei Categories: gr-qc Comments: 10 pages, 5 figures, revtex4 \\ Unparticle physics has been an active field since the seminal works of Georgi. Recently, many constraints on unparticle from various observations were considered in the literature. In particular, the cosmological constraints on unparticle dark component put it in a serious situation. In the present work, we try to find a way out of this serious situation, by including the interaction between dark energy and unparticle dark component. \\ ( http://arxiv.org/abs/0812.4489 , 247kb) ------------------------------------------------------------------------------ \\ arXiv:0812.4515 Date: Wed, 24 Dec 2008 10:18:27 GMT (10kb) Title: Quantum Black Holes. Black Hole Temperature without a Black Hole Authors: Victor Berezin (Institute for Nuclear Research, Russian Academy of Sciences) Categories: gr-qc Comments: revtex4, 7 pages, Talk given at Workshop "Black Holes in General Relativity and String Theory", August, 24-30, 2008, Veli Losinj, Croatia \\ The model is constructed, some features of which comes from quantum thin dust shells and is, in fact, an extension of the "no hair" property of classical black hole on a quantum level. It appears that the proposed classical analog of quantum black hole is heated, the temperature being exactly the Hawking's temperature. \\ ( http://arxiv.org/abs/0812.4515 , 10kb) ------------------------------------------------------------------------------ \\ arXiv:0812.4516 Date: Wed, 24 Dec 2008 10:54:34 GMT (11kb) Title: Semiclassical backreaction around a nearly spinning cosmic string Authors: Vitorio A. De Lorenci, Edisom S. Moreira Jr. (Itajuba' Federal U.) Categories: gr-qc Comments: 5 pages, no figures, REVTeX4 file \\ This paper investigates semiclassical backreaction of a conformally coupled massless scalar field on the geometrical background of a nearly spinning cosmic string - the spin density is smaller than, but arbitrarily close to, the dislocation parameter. As the spin density approaches the dislocation parameter, it is shown that an "ergoregion" spreads around the cosmic string, boosting along the string axis the once static observers. Considering that the geometrical background contains closed timelike curves when the spin density exceeds the dislocation parameter, it is argued that the appearance of the "ergoregion" may be part of a chronology protection mechanism that takes place in related non stationary geometries. \\ ( http://arxiv.org/abs/0812.4516 , 11kb) %-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%- ------------------------------------------------------------------------------ \\ arXiv:0812.2297 (*cross-listing*) Date: Fri, 12 Dec 2008 06:52:34 GMT (255kb) Date (revised v2): Wed, 24 Dec 2008 05:24:33 GMT (255kb) Title: The Role of Angular Momentum and Cosmic Censorship in the (2+1)-Dimensional Rotating Shell Collapse Authors: Robert B. Mann, John J. Oh, and Mu-In Park Categories: hep-th astro-ph gr-qc Comments: Added reference and its associated comment \\ We study the gravitational collapse problem of rotating shells in three-dimensional Einstein gravity with and without a cosmological constant. Taking the exterior and interior metrics to be those of stationary metrics with asymptotically constant curvature, we solve the equations of motion for the shells from the Darmois-Israel junction conditions in the co-rotating frame. We study various collapse scenarios with arbitrary angular momentum for a variety of geometric configurations, including anti-de Sitter, de Sitter, and flat spaces. We find that the collapsing shells can form a BTZ black hole, a three-dimensional Kerr-dS spacetime, and an horizonless geometry of point masses under certain initial conditions. For pressureless dust shells, the curvature singularity is not formed due to the angular momentum barrier near the origin. However when the shell pressure is nonvanishing, we find that for all types of shells with polytropic-type equations of state (including the perfect fluid and the generalized Chaplygin gas), collapse to a naked singularity is possible under generic initial conditions. Angular momentum does not in general guard against violation of cosmic censorship. \\ ( http://arxiv.org/abs/0812.2297 , 255kb) ------------------------------------------------------------------------------ \\ arXiv:0812.3952 (*cross-listing*) Date: Sat, 20 Dec 2008 09:35:33 GMT (60kb) Title: Non-extensive statistics in stringy space-time foam models Authors: Nick E. Mavromatos and Sarben Sarkar Categories: hep-th gr-qc Comments: 4 figures \\ The possibility of generation of non-extensive statistics, in the sense of Tsallis, due to space-time foam is discussed within the context of a particular kind of foam in string/brane-theory, the D-particle foam model . The latter involves point-like brane defects (D-particles), which provide the topologically non-trivial foamy structures of space-time. A stochastic Langevin equation for the velocity recoil of D-particles can be derived from the pinched approximation for a sum over genera in the calculation of the partition function of a bosonic string in the presence of heavy D-particles. The string coupling in standard perturbation theory is related to the exponential of the expectation of the dilaton. Inclusion of fluctuations of the dilaton itself and uncertainties in the string background will then necessitate fluctuations in $g_{s}$. The fluctuation in the string coupling in the sum over genera typically leads to a generic structure of the Langevin equation where the coefficient of the noise term, dependent on the string coupling $g_{s}$, fluctuates. The positivity of $g_{s}$ leads naturally to a stochastic modelling of its distribution with a $\chi$- distribution. This then rigorously implies a Tsallis type non-extensive or, more generally, a superstatistics distribution for the velocity recoil of D-particles. \\ ( http://arxiv.org/abs/0812.3952 , 60kb) ------------------------------------------------------------------------------ \\ arXiv:0812.4001 (*cross-listing*) Date: Sat, 20 Dec 2008 21:16:28 GMT (17kb) Title: A symmetrization of the relativistic Euler equations in several spatial variables Authors: Philippe G. LeFloch and Seiji Ukai Categories: math.AP gr-qc math.NA Comments: 19 pages MSC-class: 35L65; 76N10 \\ We consider the Euler equations governing relativistic compressible fluids evolving in the Minkowski spacetime with several spatial variables. We propose a new symmetrization which makes sense for solutions containing vacuum states and, for instance, applies to the case of compactly supported solutions, which are important to model star dynamics. Then, relying on these symmetrization and assuming that the velocity does not exceed some threshold and remains bounded away from the light speed, we deduce a local-in-time existence result for solutions containing vacuum states. We also observe that the support of compactly supported solutions does not expand as time evolves. \\ ( http://arxiv.org/abs/0812.4001 , 17kb) ------------------------------------------------------------------------------ \\ arXiv:0812.4311 (*cross-listing*) Date: Mon, 22 Dec 2008 23:54:56 GMT (10kb) Title: General Relativity with small cosmological constant from spontaneous compactification of Lovelock theory in vacuum Authors: Fabrizio Canfora, Alex Giacomini, Ricardo Troncoso and Steven Willison Categories: hep-th gr-qc Comments: 11 pages, no figures, Merry Christmas Report-no: CECS-PHY-08/10 \\ It is shown that Einstein gravity in four dimensions with small cosmological constant and small extra dimensions can be obtained by spontaneous compactification of Lovelock gravity in vacuum. Assuming that the extra dimensions are compact spaces of constant curvature, General Relativity is recovered within certain class of Lovelock theories possessing necessarily cubic or higher order terms in curvature. This bounds the higher dimension to be at least seven. Remarkably, the effective gauge coupling and Newton constant in four dimensions are not proportional to the gravitational constant in higher dimensions, but shifted with respect to their standard values. This effect opens up new scenarios where a maximally symmetric solution in higher dimensions could decay into the compactified spacetime either by tunneling or through a gravitational analogue of ghost condensation. Indeed, this is what occurs requiring both the extra dimensions and the four-dimensional cosmological constant to be small. \\ ( http://arxiv.org/abs/0812.4311 , 10kb) ------------------------------------------------------------------------------ \\ arXiv:0812.4326 (*cross-listing*) Date: Tue, 23 Dec 2008 02:21:48 GMT (46kb) Title: Accelerating Universe from Modified Kasner Model in Extra Dimensions Authors: Masato Ito Categories: hep-th astro-ph gr-qc hep-ph Comments: 14 pages, 6 figures Report-no: AUE 08-01 \\ We find the power-law solutions in (4+n)-dimensional cosmology withtime-varying cosmological constant and study the phase of cosmicevolution.The model corresponds to the modification of the higher dimensional vacuum Kasner model. When a dimensionfull parameter in the model takes special value, it is shown that 4-dimensional universe is accelerated expansion. \\ ( http://arxiv.org/abs/0812.4326 , 46kb) %%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%% ------------------------------------------------------------------------------ \\ arXiv:0807.0937 replaced with revised version Tue, 23 Dec 2008 23:38:43 GMT (501kb) Title: Breakdown of Lorentz Invariance for Spin-1/2 Particle Motion in Curved Space-Time with Applications to Muon Decay Authors: Dinesh Singh, Nader Mobed Categories: gr-qc hep-ph hep-th Comments: 19 pages, 15 figures; REVTeX file; v4. referees' comments addressed and references added; Accepted for publication in Phys. Rev. D \\ ( http://arxiv.org/abs/0807.0937 , 501kb) ------------------------------------------------------------------------------ \\ arXiv:0809.1255 replaced with revised version Tue, 23 Dec 2008 22:00:49 GMT (8kb) Title: Decay of the free-theory vacuum of scalar field theory in de Sitter spacetime in the interaction picture Authors: Atsushi Higuchi Categories: gr-qc hep-th Comments: title changed, 7 pages \\ ( http://arxiv.org/abs/0809.1255 , 8kb) ------------------------------------------------------------------------------ \\ arXiv:0811.0756 replaced with revised version Wed, 24 Dec 2008 20:36:53 GMT (10kb) Title: On the recently determined anomalous perihelion precession of Saturn Authors: Lorenzo Iorio Categories: gr-qc astro-ph hep-ph physics.space-ph Comments: LaTex2e, 14 pages, no figures, 2 tables. Accepted by The Astronomical Journal (AJ) \\ ( http://arxiv.org/abs/0811.0756 , 10kb) %%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%--- 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