Date: Tue, 5 Mar 2002 20:24:04 -0500 From: no-reply@arXiv.org (send mail ONLY to gr-qc) To: rabble@arXiv.org (gr-qc daily title/abstract distribution) Subject: gr-qc daily 0203014 -- 0203016 received 26 Message-Id: <200203060124.g261O4d25507@xxx.arxiv.cornell.edu> MIME-Version: 1.0 ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ send mail only to gr-qc@arXiv.org, do not reply to no-reply@arXiv.org . send any complaints regarding submissions directly to submitter. use a single `get' to request multiple papers, `list macros' for available macro packages, and `help' for a list of available commands and other info. ------------------------------------------------------------------------------ point your www client at http://arXiv.org/ To unsubscribe, e-mail To: gr-qc@arXiv.org, Subject: cancel ------------------------------------------------------------------------------ received from Mon 4 Mar 02 21:00:00 GMT to Tue 5 Mar 02 21:00:00 GMT ------------------------------------------------------------------------------ \\ Paper: gr-qc/0203014 From: Michele Vallisneri Date: Mon, 4 Mar 2002 23:42:18 GMT (36kb) Title: Ephemeral point-events: is there a last remnant of physical objectivity? Authors: Massimo Pauri and Michele Vallisneri Comments: LaTeX, natbib, 34 pages. To be published in the Roberto Torretti Festschrift, Dialogos (2002) \\ For the past two decades, Einstein's Hole Argument (which deals with the apparent indeterminateness of general relativity due to the general covariance of the field equations) and its resolution in terms of Leibniz equivalence (the statement that Riemannian geometries related by active diffeomorphisms represent the same physical solution) have been the starting point for a lively philosophical debate on the objectivity of the point-events of space-time. It seems that Leibniz equivalence makes it impossible to consider the points of the space-time manifold as physically individuated without recourse to dynamical individuating fields. Various authors have posited that the metric field itself can be used in this way, but nobody so far has considered the problem of explicitly distilling the metrical fingerprint of point-events from the gauge-dependent components of the metric field. Working in the Hamiltonian formulation of general relativity, and building on the results of Lusanna and Pauri (2002), we show how Bergmann and Komar's intrinsic pseudo-coordinates (based on the value of curvature invariants) can be used to provide a physical individuation of point-events in terms of the true degrees of freedom (the Dirac observables) of the gravitational field, and we suggest how this conceptual individuation could in principle be implemented with a well-defined empirical procedure. We argue from these results that point-events retain a significant kind of physical objectivity. \\ ( http://arXiv.org/abs/gr-qc/0203014 , 36kb) ------------------------------------------------------------------------------ \\ Paper: gr-qc/0203015 From: Reg Cahill Date: Tue, 5 Mar 2002 04:41:44 GMT (48kb) Title: Process Physics: From Quantum Foam to General Relativity Authors: Reginald T. Cahill Comments: 26 pages Latex, 1 separate eps file \\ Progress in the new information-theoretic process physics is reported in which the link to the phenomenology of general relativity is made. In process physics the fundamental assumption is that reality is to be modelled as self-organising semantic (or internal or relational) information using a self-referentially limited neural network model. Previous progress in process physics included the demonstration that space and quantum physics are emergent and unified, with time a distinct non-geometric process, that quantum phenomena are caused by fractal topological defects embedded in and forming a growing three-dimensional fractal process-space, which is essentially a quantum foam. Other features of the emergent physics were: quantum field theory with emergent flavour and confined colour, limited causality and the Born quantum measurement metarule, inertia, time-dilation effects, gravity and the equivalence principle, a growing universe with a cosmological constant, black holes and event horizons, and the emergence of classicality. Here general relativity and the technical language of general covariance is seen not to be fundamental but a phenomenological construct, arising as an amalgam of two distinct phenomena: the `gravitational' characteristics of the emergent quantum foam for which `matter' acts as a sink, and the classical `spacetime' measurement protocol, but with the later violated by quantum measurement processes. Quantum gravity, as manifested in the emergent Quantum Homotopic Field Theory of the process-space or quantum foam, is logically prior to the emergence of the general relativity phenomenology, and cannot be derived from it. \\ ( http://arXiv.org/abs/gr-qc/0203015 , 48kb) ------------------------------------------------------------------------------ \\ Paper: gr-qc/0203016 From: Sawa Manoff Date: Tue, 5 Mar 2002 10:20:39 GMT (30kb) Title: Mechanics of Continuous Media in $(\bar{L}_n,g)$-spaces. I. Introduction and mathematical tools Authors: Sawa Manoff Comments: 34 pages, LaTeX \\ Basic notions and mathematical tools in continuum media mechanics are recalled. The notion of exponent of a covariant differential operator is introduced and on its basis the geometrical interpretation of the curvature and the torsion in $(\bar{L}_n,g)$-spaces is considered. The Hodge (star) operator is generalized for $(\bar{L}_n,g)$-spaces. The kinematic characteristics of a flow are outline in brief. PACS numbers: 11.10.-z; 11.10.Ef; 7.10.+g; 47.75.+f; 47.90.+a; 83.10.Bb \\ ( http://arXiv.org/abs/gr-qc/0203016 , 30kb) %-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%-%- ------------------------------------------------------------------------------ \\ Paper (*cross-listing*): astro-ph/0203043 From: (Giallo) Israel Date: Mon, 4 Mar 2002 18:37:54 GMT (115kb) Title: RXJ0806.3+1527: a double degenerate binary with the shortest known orbital period (321s) Authors: G.L. Israel, W. Hummel, S. Covino, S. Campana, I. Appenzeller, W. Gassler, K.-H. Mantel, G. Marconi, C.W. Mauche, U. Munari, I. Negueruela, H. Nicklas, G. Rupprecht, R.L. Smart, O. Stahl, L. Stella Comments: Accepted for publication on A&A Letters \\ We carried out optical observations of the field of the X-ray pulsator RXJ0806.3+1527. A blue V=21.1 star was found to be the only object consistent with the X-ray position. VLT FORS spectra revealed a blue continuum with no intrinsic absorption lines. Broad (v~1500 km/s), low equivalent width (about -1/-6A) emission lines from the HeII Pickering series were clearly detected. B, V and R time-resolved photometry revealed the presence of about 15% pulsations at the 321s X-ray period, confirming the identification. These findings, together with the period stability and absence of any additional modulation in the 1min-5hr period range, argue in favour of the orbital interpretation of the 321s pulsations. The most likely scenario is thus that RXJ0806.3+1527 is a double degenerate system of the AM CVn class. This would make RXJ0806.3+1527 the shortest orbital period binary currently known and one of the best candidates for gravitational wave detection. \\ ( http://arXiv.org/abs/astro-ph/0203043 , 115kb) ------------------------------------------------------------------------------ \\ Paper (*cross-listing*): hep-th/0203003 From: Amir Masoud Ghezelbash Date: Thu, 28 Feb 2002 22:14:05 GMT (26kb) Title: Vortices in De Sitter Spacetimes Authors: A.M. Ghezelbash, R.B. Mann Comments: 11 pages, 5 figures Report-no: WATPPHYS-TH02/02 \\ We investigate vortex solutions to the Abelian Higgs field equations in a four dimensional de Sitter spacetime background. We obtain both static and dynamic solutions with axial symmetry that are generalizations of the Nielsen-Olesen gauge vortices in flat spacetime. The static solution is located in the static patch of de Sitter space. We numerically solve the field equations in an inflationary (big bang) patch and find a time dependent vortex soution. We show that the effect of the vortex is to create a deficit angle in the spacetime. We comment on the relationship of these solutions to their anti de Sitter counterparts, and on their possible holographic interpretation. \\ ( http://arXiv.org/abs/hep-th/0203003 , 26kb) ------------------------------------------------------------------------------ \\ Paper (*cross-listing*): hep-th/0203013 From: Patrick Peter Date: Fri, 1 Mar 2002 18:04:07 GMT (261kb) Title: Primordial perturbations in a non singular bouncing universe model Authors: Patrick Peter (IAP) and Nelson Pinto-Neto (CBPF) Comments: 11 pages, RevTeX 4, 8 figures, submitted to Phys. Rev. D \\ We construct a simple non singular cosmological model in which the currently observed expansion phase was preceded by a contraction. This is achieved, in the framework of pure general relativity, by means of a radiation fluid and a free scalar field having negative energy. We calculate the power spectrum of the scalar perturbations that are produced in such a bouncing model and find that, under the assumption of initial vacuum state for the quantum field associated with the hydrodynamical perturbation, this leads to a spectral index n=-1. The matching conditions applying to this bouncing model are derived and shown to be different from those in the case of a sharp transition. We find that if our bounce transition can be smoothly connected to a slowly contracting phase, then the resulting power spectrum will be scale invariant. \\ ( http://arXiv.org/abs/hep-th/0203013 , 261kb) %%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%%--%% ------------------------------------------------------------------------------ \\ Paper: gr-qc/0110010 replaced with revised version Tue, 5 Mar 2002 17:19:56 GMT (13kb) Title: Radiation from perfect mirrors starting from rest and the black body spectrum Authors: A. Calogeracos (Division of Theoretical Mechanics, Hellenic Air Force Academy, Greece) Comments: Typos corrected \\ ( http://arXiv.org/abs/gr-qc/0110010 , 13kb) %%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%---%%%--- 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. 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