1,720,976 research outputs found
Tackling conceptual problems in gravity with numerically simulated gedanken experiments
Full text linkGedanken experiments, also known as thought experiments, are an extremely powerful tool for studying conceptual problems in physics. The strategy is to devise fictitious experimental setups in which the effects one is interested in investigating clearly manifest, and can be better analyzed. In some cases it is necessary to predict the evolution of physical systems, a task that can become particularly hard when the theory is nonlinear. A possible approach to solve this issue is to perform a numerical integration of the evolution equations, thus simulating the gedanken experiment. In this thesis I will present three works, that I have carried out with different collaborators, in which such research technique has been used to tackle conceptual problems of different nature. In particular, in the first we performed extensive numerical simulations of the collapse of charged wave packets in Einstein-Maxwell and in Einstein-Maxwell-scalar theories of gravity, in the attempt of forming naked singularities and violate the weak cosmic censorship conjecture. In the second work we studied the fate of minimum mass black hole in Einstein-dilaton-Gauss-Bonnet gravity, when they undergo Hawking evaporation, by constructing a numerically simulated gedanken experiment in which we dynamically reduced the black hole mass by means of wave packets of a phantom field. Lastly, in the third work we simulated the nonlinear interaction between high-amplitude, low-frequency electromagnetic wave packets and a barrier of plasma, with the purpose of studying whether, in the scenario of the plasma-driven superradiant instability, the electromagnetic field can be confined in the vicinity of the black hole even during its exponential growth
Black holes in a box
Full text linkThe evolution of BHs in "confining boxes" is interesting for a number of reasons, particularly because it mimics some aspects of anti-de Sitter spacetimes. These admit no Cauchy surface and are a simple example of a non-globally hyperbolic spacetime. We are here interested in the potential role that boundary conditions play in the evolution of a BH system. For that, we imprison a binary BH in a box, at which boundary we set mirror-like boundary conditions. © 2010 IOP Publishing Ltd
Numerical relativity in higher dimensions
Full text linkWe give a status report on our project targeted at performing numerical simulations of a head-on collision of non-spinning black holes in higher dimensional non-compact space-times. These simulations should help us understand black objects in higher dimensions and their stability properties. They are also relevant for the problem of black hole formation and evaporation in particle accelerators and cosmic rays. We use the symmetries of the system to reduce the problem to an effective 3+1 problem, allowing the use of existing numerical codes. As a simple application of the formalism, we present the results for the evolution of a five dimensional single black hole space-time. © 2010 IOP Publishing Ltd
Numerical relativity for D dimensional axially symmetric space-times: Formalism and code tests
Full text linkThe numerical evolution of Einstein's field equations in a generic background has the potential to answer a variety of important questions in physics: from applications to the gauge-gravity duality, to modeling black hole production in TeV gravity scenarios, to analysis of the stability of exact solutions, and to tests of cosmic censorship. In order to investigate these questions, we extend numerical relativity to more general space-times than those investigated hitherto, by developing a framework to study the numerical evolution of D dimensional vacuum space-times with an SO(D - 2) isometry group for D >= 5, or SO(D - 3) for D >= 6. Performing a dimensional reduction on a (D - 4) sphere, the D dimensional vacuum Einstein equations are rewritten as a 3 + 1 dimensional system with source terms, and presented in the Baumgarte, Shapiro, Shibata, and Nakamura formulation. This allows the use of existing 3 + 1 dimensional numerical codes with small adaptations. Brill-Lindquist initial data are constructed in D dimensions and a procedure to match them to our 3 + 1 dimensional evolution equations is given. We have implemented our framework by adapting the LEAN code and perform a variety of simulations of nonspinning black hole space-times. Specifically, we present a modified moving puncture gauge, which facilitates long-term stable simulations in D = 5. We further demonstrate the internal consistency of the code by studying convergence and comparing numerical versus analytic results in the case of geodesic slicing for D = 5, 6
Numerical relativity for D dimensional space-times: Head-on collisions of black holes and gravitational wave extraction
Full text linkHigher dimensional black holes play an exciting role in fundamental physics, such as high energy physics. In this paper, we use the formalism and numerical code reported in [1] to study the head-on collision of two black holes. For this purpose we provide a detailed treatment of gravitational wave extraction in generic D dimensional space-times, which uses the Kodama-Ishibashi formalism. For the first time, we present the results of numerical simulations of the head-on collision in five space-time dimensions, together with the relevant physical quantities. We show that the total radiated energy, when two black holes collide from rest at infinity, is approximately (0.089 +/- 0.006)% of the center of mass energy, slightly larger than the 0.055% obtained in the four-dimensional case, and that the ringdown signal at late time is in very good agreement with perturbative calculations
Head-on collisions of unequal mass black holes in D=5 dimensions
Full text linkWe study head-on collisions of unequal mass black hole binaries in D = 5 spacetime dimensions, with mass ratios between 1:1 and 1:4. Information about gravitational radiation is extracted by using the Kodama-Ishibashi gauge-invariant formalism and details of the apparent horizon of the final black hole. We present waveforms, total integrated energy and momentum for this process. Our results show surprisingly good agreement, within 5% or less, with those extrapolated from linearized, point-particle calculations. Our results also show that consistency with the area theorem bound requires that the same process in a large number of spacetime dimensions must display new features
Dynamics of black holes in de Sitter spacetimes
Full text linkNonlinear dynamics in cosmological backgrounds has the potential to teach us immensely about our Universe, and also to serve as prototype for nonlinear processes in generic curved spacetimes. Here we report on dynamical evolutions of black holes in asymptotically de Sitter spacetimes. We focus on the head-on collision of equal mass binaries and for the first time compare analytical and perturbative methods with full blown nonlinear simulations. Our results include an accurate determination of the merger/scatter transition (consequence of an expanding background) for small mass binaries and a test of the cosmic censorship conjecture, for large mass binaries. We observe that, even starting from small separations, black holes in large mass binaries eventually lose causal contact, in agreement with the conjecture
Black Hole Collisions in Asymptotically de Sitter SpacetimesRelativity and Gravitation
No full textWe report on the first dynamical evolutions of black holes in asymptotically de Sitter spacetimes. We focus on the head-on collision of equal mass binaries and compare analytical and perturbative methods with full blown nonlinear simulations. Our results include an accurate determination of the merger/scatter transition (consequence of an expanding background) for small mass binaries and a test of the Cosmic Censorship conjecture, for large mass binaries. We observe that, even starting from small separations, black holes in large mass binaries eventually lose causal contact, in agreement with the conjecture
Numerical Relativity in D dimensional space-times: Collisions of unequal mass black holes
Full text linkWe present unequal mass head-on collisions of black holes in D = 5 dimensional space-times. We have simulated BH systems with mass ratios q = 1,1/2,1/3,1/4. We extract the total energy radiated throughout the collision and compute the linear momentum flux and the recoil velocity of the final black hole. The numerical results show very good agreement with point particle calculations when extrapolated to this limit
Higher-dimensional puncture initial data
Full text linkWe calculate puncture initial data, corresponding to single and binary black holes with linear momenta, which solve the constraint equations of D-dimensional vacuum gravity. The data are generated by a modification of the pseudospectral code presented in [M. Ansorg, B. Bruegmann, and W. Tichy, Phys. Rev. D 70, 064011 (2004).] and made available as the TWOPUNCTURES thorn inside the CACTUS computational toolkit. As examples, we exhibit convergence plots, the violation of the Hamiltonian constraint as well as the initial data for D = 4, 5, 6, 7. These initial data are the starting point to perform high-energy collisions of black holes in D dimensions
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