oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Any time

2020 ( 28 )

2019 ( 356 )

2018 ( 1901 )

2017 ( 1799 )

Custom range...

Search Results: 1 - 10 of 120141 matches for " Anzhong Wang "
All listed articles are free for downloading (OA Articles)
Page 1 /120141
Display every page Item
Critical Phenomena in Gravitational Collapse: The Studies So Far
Wang, Anzhong;
Brazilian Journal of Physics , 2001, DOI: 10.1590/S0103-97332001000200009
Abstract: studies of black hole formation from gravitational collapse have revealed interesting non-linear phenomena at the threshold of black hole formation. in particular, in 1993 choptuik studied the collapse of a massless scalar field with spherical symmetry and found some behaviour, which is quite similar to the critical phenomena well-known in statistical mechanics and quantum field theory. universality and echoing of the critical solution and power-law scaling of the black hole masses have given rise to the name critical phenomena in gravitational collapse. choptuik's results were soon confirmed both numerically and semi-analytically, and have extended to various other matter fields. in this paper, we shall give a brief introduction to this fascinating and relatively new area, and provide an updated publication list. an analytical "toy" model of critical collapse is presented, and some current investigations are given.
Critical Phenomena in Gravitational Collapse: The Studies So Far
Wang Anzhong
Brazilian Journal of Physics , 2001,
Abstract: Studies of black hole formation from gravitational collapse have revealed interesting non-linear phenomena at the threshold of black hole formation. In particular, in 1993 Choptuik studied the collapse of a massless scalar field with spherical symmetry and found some behaviour, which is quite similar to the critical phenomena well-known in Statistical Mechanics and Quantum Field Theory. Universality and echoing of the critical solution and power-law scaling of the black hole masses have given rise to the name Critical Phenomena in Gravitational Collapse. Choptuik's results were soon confirmed both numerically and semi-analytically, and have extended to various other matter fields. In this paper, we shall give a brief introduction to this fascinating and relatively new area, and provide an updated publication list. An analytical "toy" model of critical collapse is presented, and some current investigations are given.
Critical collapse in tensor-multi-scalar and non-linear gravity theories: A universal class
Anzhong Wang
Physics , 1999,
Abstract: Critical collapse in tensor-multi-scalar gravity theories is studied, and found that for any given target space all the theories conformally related belong to the same universal class. When only one scalar field is present, the universality is extended to include a class of non-linear gravity theories.
Comment on "Absence of trapped surfaces and singularities in cylindrical collapse"
Anzhong Wang
Physics , 2003, DOI: 10.1103/PhysRevD.72.108501
Abstract: Recently, the gravitational collapse of an infinite cylindrical thin shell of matter in an otherwise empty spacetime with two hypersurface orthogonal Killing vectors was studied by Gon\c{c}alves [Phys. Rev. {\bf D65}, 084045 (2002).]. By using three "alternative" criteria for trapped surfaces, the author claimed to have shown that {\em they can never form either outside or on the shell, regardingless of the matter content for the shell, except at asymptotical future null infinite}. Following Penrose's original idea, we first define trapped surfaces in cylindrical spacetimes in terms of the expansions of null directions orthogonal to the surfaces, and then show that the first criterion used by Gon\c{c}alves is incorrect. We also show that his analysis of non-existence of trapped surfaces in vacuum is incomplete. To confirm our claim, we present an example that is a solution to the vacuum Einstein field equations and satisfies all the regular conditions imposed by Gon\c{c}alves. After extending the solution to the whole spacetime, we show explicitly that trapped surfaces exist in the extended region.
$f(R)$ theory and geometric origin of the dark sector in Horava-Lifshitz gravity
Anzhong Wang
Physics , 2010, DOI: 10.1142/S0217732311034980
Abstract: Inclusion of $f(R)$ term in the action of Horava-Lifshitz quantum gravity with projectability but without detailed balance condition is investigated, where $R$ denotes the 3-spatial dimensional Ricci scalar. Conditions for the spin-0 graviton to be free of ghosts and instability are studied. The requirement that the theory reduce to general relativity in the IR makes the scalar mode unstable in the Minkowski background but stable in the de Sitter. It is remarkable that the dark sector, dark matter and dark energy, of the universe has a naturally geometric origin in such a setup. Bouncing universes can also be constructed. Scalar perturbations in the FRW backgrounds with non-zero curvature are presented.
Orbifold branes in string/M-Theory and their cosmological applications
Anzhong Wang
Physics , 2010,
Abstract: In this brief report, we summarize our recent studies in brane cosmology in both string theory and M-Theory on $S^{1}/Z_{2}$. In such setups, we find that the radion is stable and its mass, with a very conservative estimation, can be of the order of $0. 1 \sim 0.01$ GeV. The hierarchy problem can be addressed by combining the large extra dimension, warped factor, and tension coupling mechanisms. Gravity is localized on the visible brane, and the spectrum of the gravitational Kaluza-Klein (KK) modes is discrete and can have a mass gap of TeV. The corrections to the 4D Newtonian potential from the higher order gravitational KK modes are exponentially suppressed. Applying such setups to cosmology, we find that a late transient acceleration of the universe seems to be the generic feature of the theory, due to the interaction between branes and bulk. A bouncing early universe is also rather easily realized.
Vector and tensor perturbations in Horava-Lifshitz cosmology
Anzhong Wang
Physics , 2010, DOI: 10.1103/PhysRevD.82.124063
Abstract: We study cosmological vector and tensor perturbations in Horava-Lifshitz gravity, adopting the most general Sotiriou-Visser-Weinfurtner generalization without the detailed balance but with projectability condition. After deriving the general formulas in a flat FRW background, we find that the vector perturbations are identical to those given in general relativity. This is true also in the non-flat cases. For the tensor perturbations, high order derivatives of the curvatures produce effectively an anisotropic stress, which could have significant efforts on the high-frequency modes of gravitational waves, while for the low-frenquency modes, the efforts are negligible. The power spectrum is scale-invariant in the UV regime, because of the particular dispersion relations. But, due to lower-order corrections, it will eventually reduce to that given in GR in the IR limit. Applying the general formulas to the de Sitter and power-law backgrounds, we calculate the power spectrum and index, using the uniform approximations, and obtain their analytical expressions in both cases.
Thick de Sitter 3-Branes, Dynamic Black Holes and Localization of Gravity
Anzhong Wang
Physics , 2002, DOI: 10.1103/PhysRevD.66.024024
Abstract: The embedding of a thick de Sitter 3-brane into a five-dimensional bulk is studied, assuming a scalar field with potential is present in the bulk. A class of solutions is found in closed form that can represent a thick de Sitter 3-brane interpolating either between two dynamical black holes with a $R \times S_{4}$ topology or between two Rindler-like spacetimes with a $R_{2}\times S_{3}$ topology. The gravitational field is localized in a small region near the center of the 3-brane. The analysis of graviton fluctuations shows that a zero mode exists and separates itself from a set of continuous modes by a mass gap. The existence of such a mass gap is shown to be universal. The scalar perturbations are also studied and shown to be stable.
No-Go Theorem in Spacetimes with Two Commuting Spacelike Killing Vectors
Anzhong Wang
Physics , 2003, DOI: 10.1007/s10714-005-0166-0
Abstract: Four-dimensional Riemannian spacetimes with two commuting spacelike Killing vectors are studied in Einstein's theory of gravity, and found that no outer apparent horizons exist, provided that the dominant energy condition holds.
Critical Collapse of Cylindrically Symmetric Scalar Field in Four-Dimensional Einstein's Theory of Gravity
Anzhong Wang
Physics , 2003, DOI: 10.1103/PhysRevD.68.064006
Abstract: Four-dimensional cylindrically symmetric spacetimes with homothetic self-similarity are studied in the context of Einstein's Theory of Gravity, and a class of exact solutions to the Einstein-massless scalar field equations is found. Their local and global properties are investigated and found that they represent gravitational collapse of a massless scalar field. In some cases the collapse forms black holes with cylindrical symmetry, while in the other cases it does not. The linear perturbations of these solutions are also studied and given in closed form. From the spectra of the unstable eigen-modes, it is found that there exists one solution that has precisely one unstable mode, which may represent a critical solution, sitting on a boundary that separates two different basins of attraction in the phase space.
Page 1 /120141
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.