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| General Relativity and Quantum Cosmology : Introduction to Quantum Fields in Curved Spacetime and the Hawking Effect |
| gr-qc/0308048 (August 2003) | | Introduction to Quantum Fields in Curved Spacetime and the Hawking Effect | | Ted Jacobson | | Received. 14 August 2003 Last updated. 09 April 2004 | | Abstract. These notes introduce the subject of quantum field theory in curved spacetime and some of its applications and the questions they raise. Topics include particle creation in time-dependent metrics, quantum origin of primordial perturbations, Hawking effect, the trans-Planckian question, and Hawking radiation on a lattice. | | Categories. gr-qc hep-th | | Comment. Based on lectures given at the CECS School on Quantum Gravity in Valdivia, Chile, January 2002, 59 pages, 5 figures; v2 improved explanation of use of analyticity in Hawking effect derivation; v3 typo fixed in Fig.2 |
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| General Relativity and Quantum Cosmology : Gaussian superpositions in scalar-tensor quantum cosmological models |
| gr-qc/0005013 (May 2000) | | Gaussian superpositions in scalar-tensor quantum cosmological models | | R. Colistete Jr., J. C. Fabris and N. Pinto-Neto | | Received. 03 May 2000 Last updated. 03 May 2000 | | Abstract. A free scalar field minimally coupled to gravity model is quantized and the Wheeler-DeWitt equation in minisuperspace is solved analytically, exhibiting positive and negative frequency modes. The analysis is performed for positive, negative and zero values of the curvature of the spatial section. Gaussian superpositions of the modes are constructed, and the quantum bohmian trajectories are determined in the framework of the Bohm-de Broglie interpretation of quantum cosmology. Oscillating universes appear in all cases, but with a characteristic scale of the order of the Planck scale. Bouncing regular solutions emerge for the flat curvature case. They contract classically from infinity until a minimum size, where quantum effects become important acting as repulsive forces avoiding the singularity and creating an inflationary phase, expanding afterwards to an infinite size, approaching the classical expansion as long as the scale factor increases. These are non-singular solutions which are viable models to describe the early Universe. | | Categories. gr-qc | | Comment. 14 pages, LaTeX, 3 Postscript figures, uses graficx.sty | | Journal-ref. Phys.Rev. D62 (2000) 083507 | | Published Article doi: 10.1103/PhysRevD.62.083507 |
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| General Relativity and Quantum Cosmology : Energy and Angular Momentum Densities in a Godel-Type Universe in the Teleparallel Geometry |
| arXiv:0803.1481 (March 2008) | | Energy and Angular Momentum Densities in a Godel-Type Universe in the Teleparallel Geometry | | A. A. Sousa, R. B. Pereira and A. C. Silva | | Received. 10 March 2008 Last updated. 10 March 2008 | | Abstract. The main scope in this research consisted in evaluating the total energy-momentum and gravitational angular momentum densities in this universe with global rotation. For that, we use the Hamiltonian formalism of the Teleparallel Equivalent of General Relativity (TEGR), justified for presenting covariant expressions for the considered quantities. Our result for the energy-momentum density (irrespective of the equations of state of the cosmic fluid) is not totally in accord with the results reported by other authors in the literature using pseudotensors, differing by a constant factor. We also show the equivalence among the field equations of the TEGR and Einstein equations (RG), considering a perfect fluid and Godel-Obukov metric. | | Categories. gr-qc | | Comment. 20 pages, no figures License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
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| General Relativity and Quantum Cosmology : Hawking radiation of Dirac particles via tunneling from Kerr black hole |
| arXiv:0803.1410 (March 2008) | | Hawking radiation of Dirac particles via tunneling from Kerr black hole | | Ran Li and Ji-Rong Ren | Institute of Theoretical Physics, Lanzhou University, Lanzhou, 730000, Gansu, China
| | Received. 10 March 2008 Last updated. 10 March 2008 | | Abstract. We investigated Dirac Particles' Hawking radiation from event horizon of Kerr black hole in terms of the tunneling formalism. Applying WKB approximation to the general covariant Dirac equation in Kerr spacetime background, we obtain the tunneling probability for fermions and Hawking temperature of Kerr black hole. The result obtained by taking the fermion tunneling into account is consistent with the previous literatures. | | Categories. gr-qc | | Comment. 7 pages, no figures License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
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| General Relativity and Quantum Cosmology : On the curvature of the present-day Universe |
| arXiv:0803.1401 (March 2008) | | On the curvature of the present-day Universe | | Thomas Buchert and Mauro Carfora | Université Lyon 1, Centre de Recherche Astrophysique de Lyon, CNRS UMR 5574, quad 9 avenue Charles André, F--69230 Saint--Genis--Laval, France
Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, quad via A. Bassi 6, I--27100 Pavia, Italy Emails: buchert@obs.univ--lyon1.fr and mauro.carfora@pv.infn.it
Dipartimento di Fisica Nucleare e Teorica, Università degli Studi di Pavia, quad via A. Bassi 6, I--27100 Pavia, Italy
| | Received. 10 March 2008 Last updated. 10 March 2008 | | Abstract. We discuss the effect of curvature and matter inhomogeneities on the averaged scalar curvature of the present-day Universe. Motivated by studies of averaged inhomogeneous cosmologies, we contemplate on the question whether it is sensible to assume that curvature averages out on some scale of homogeneity, as implied by the standard concordance model of cosmology, or whether the averaged scalar curvature can be largely negative today, as required for an explanation of Dark Energy from inhomogeneities. We confront both conjectures with a detailed analysis of the kinematical backreaction term and estimate its strength for a multi-scale inhomogeneous matter and curvature distribution. Our main result is a formula for the spatially averaged scalar curvature involving quantities that are all measurable on regional (i.e. up to 100 Mpc) scales. We propose strategies to quantitatively evaluate the formula, and pinpoint the assumptions implied by the conjecture of a small or zero averaged curvature. We reach the conclusion that the standard concordance model needs fine-tuning in the sense of an assumed equipartition law for curvature in order to reconcile it with the estimated properties of the averaged physical space, whereas a negative averaged curvature is favoured, independent of the prior on the value of the cosmological constant. | | Categories. gr-qc | | Comment. 31 pages License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
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| General Relativity and Quantum Cosmology : On Hawking/Unruh Process: Where does the Radiation Come from? |
| arXiv:0803.1347 (March 2008) | | On Hawking/Unruh Process: Where does the Radiation Come from? | | Tadas K. Nakamura | CFAAS, Fukui Prefectural University, Fukui 910-1195, Japan
| | Received. 10 March 2008 Last updated. 10 March 2008 | | Abstract. The energy source of the radiation in Unruh/Hawking process is investigated with emphasis on the particle number definition based on conservation laws. It has been shown that the particle radiation is not the result of pair creation by the gravitational force, but the result of difference in the conservation laws to define the particle number. The origin of the radiated energy in the distant future corresponds to the zero point oscillations with infinitely large wave numbers. This result implies the need of reconsideration on the scenario of black hole evaporation. | | Categories. gr-qc | | Comment. 9 pages, 0 figures License: http://creativecommons.org/licenses/by/3.0/ |
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| General Relativity and Quantum Cosmology : A volume-weighted measure for eternal inflation |
| arXiv:0803.1300 (March 2008) | | A volume-weighted measure for eternal inflation | | Sergei Winitzki | Arnold Sommerfeld Center, Department of Physics, Ludwig-Maximilians University, Munich, Germany
| | Received. 10 March 2008 Last updated. 10 March 2008 | | Abstract. I propose a new volume-weighted probability measure for cosmological "multiverse" scenarios involving eternal inflation. The "reheating-volume (RV) cutoff" calculates the distribution of observable quantities on a portion of the reheating hypersurface that is conditioned to be finite. The RV measure is gauge-invariant, does not suffer from the "youngness paradox," and is independent of initial conditions at the beginning of inflation. In slow-roll inflationary models with a scalar inflaton, the RV-regulated probability distributions can be obtained by solving nonlinear diffusion equations. I discuss possible applications of the new measure to "landscape" scenarios with bubble nucleation. | | Categories. gr-qc | | Comment. 4 pages, 1 figure included License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
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| General Relativity and Quantum Cosmology : Mars and frame-dragging: study for a dedicated mission |
| arXiv:0803.1286 (March 2008) | | Mars and frame-dragging: study for a dedicated mission | | Lorenzo Iorio | | Received. 10 March 2008 Last updated. 10 March 2008 | | Abstract. In this paper we preliminarily explore the possibility of designing a dedicated satellite-based mission to measure the general relativistic gravitomagnetic Lense-Thirring effect in the gravitational field of Mars. The focus is on the systematic error induced by the multipolar expansion of the areopotential and on possible strategies to reduce it. It turns out that the major sources of bias are the Mars'equatorial radius R and the even zonal harmonics J_L, L = 2,4,6... of the areopotential. An optimal solution, in principle, consists of using two probes at high-altitudes (aapprox 9500-9600 km) and different inclinations, and suitably combining their nodes in order to entirely cancel out the bias due to delta R. The remaining uncancelled mismodelled terms due to delta J_L, L = 2,4,6,... would induce a bias lesssim 1%, according to the present-day MGS95J gravity model, over a wide range of admissible values of the inclinations. The Lense-Thirring out-of-plane shifts of the two probes would amount to about 10 cm yr^-1. | | Categories. gr-qc | | Comment. LaTex2e, 15 pages, 5 figures, no tables License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
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| General Relativity and Quantum Cosmology : On the stability of spherically symmetric spacetimes in metric f(R) gravity |
| arXiv:0803.0867 (March 2008) | | On the stability of spherically symmetric spacetimes in metric f(R) gravity | | Kimmo Kainulainen and Daniel Sunhede | Dept. of Physics, P.O. Box 35 (YFL), FI-40014 University of Jyväskylä, Finland
Helsinki Institute of Physics and Dept. of Physical Sciences, P.O. Box 64, FI-00014 University of Helsinki, Finland
| | Received. 06 March 2008 Last updated. 10 March 2008 | | Abstract. We consider stability properties of spherically symmetric spacetimes of stars in metric f(R) gravity. We stress that these not only depend on the particular model, but also on the specific physical configuration. Typically configurations giving the desired $gamma_{m PPN} approx 1$ are strongly constrained, while those corresponding to $gamma_{m PPN} approx 1/2$ are less affected. Furthermore, even when the former are found strictly stable in time, the domain of acceptable static spherical solutions typically shrinks to a point in the phase space. Unless a physical reason to prefer such a particular configuration can be found, this poses a naturalness problem for the currently known metric f(R) models for accelerating expansion of the Universe. | | Categories. gr-qc astro-ph | | Comment. Corrected affiliation, 8 pages, 3 figures License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
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| General Relativity and Quantum Cosmology : Equilibrium boundary conditions, dynamic vacuum energy, and the Big Bang |
| arXiv:0803.0281 (March 2008) | | Equilibrium boundary conditions, dynamic vacuum energy, and the Big Bang | | F. R. Klinkhamer | Institute for Theoretical Physics, University of Karlsruhe (TH), 76128 Karlsruhe, Germany
| | Received. 03 March 2008 Last updated. 10 March 2008 | | Abstract. The smallness of the cosmological constant Lambda in an equilibrium context may be due to the existence of a self-tuning vacuum variable q. Here, a nonequilibrium context is considered with a corresponding time-dependent cosmological parameter Lambda(t) or vacuum energy density ho_V(t). A specific model of a closed Friedmann-Robertson-Walker universe is presented, which is determined by equilibrium boundary conditions at one particular instant of time and an appropriate form of vacuum-energy dynamics. The model has a standard Big Bang phase at early times and reproduces the main characteristics of the present universe. | | Categories. gr-qc | | Comment. 12 pages with revtex4; v2: minor improvements | | Report No. KA-TP-06-2008 License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
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