A5071638989- Black Holes and Theoretical Physics
- Cosmology and Gravitation Theories
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Quantum Electrodynamics and Casimir Effect
- Ion-surface interactions and analysis
- Particle physics theoretical and experimental studies
- Health, Nursing, Elderly Care
- Relativity and Gravitational Theory
- Galaxies: Formation, Evolution, Phenomena
- Integrated Circuits and Semiconductor Failure Analysis
- Electron and X-Ray Spectroscopy Techniques
- Nonlinear Waves and Solitons
- Superconducting and THz Device Technology
- Fusion materials and technologies
- Dark Matter and Cosmic Phenomena
- Neutrino Physics Research
- Electric Vehicles and Infrastructure
- Algebraic structures and combinatorial models
- Silicon and Solar Cell Technologies
- Metal and Thin Film Mechanics
- Advanced Topics in Algebra
- Noncommutative and Quantum Gravity Theories
- Semiconductor materials and devices
- Transportation and Mobility Innovations
Iscte – Instituto Universitário de Lisboa
2024
Institute of Astrophysics and Space Sciences
2015-2024
University of Lisbon
2014-2024
Instituto de Telecomunicações
2011-2024
Universidade Federal do Rio de Janeiro
2021
Universitat de Barcelona
2015-2020
Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento
2013-2019
Centro de Estudos em Geografia e Ordenamento do Territorio
2018
Universidade Nova de Lisboa
2018
Instituto Superior Técnico
2009-2017
A possible process to destroy a black hole consists on throwing point particles with sufficiently large angular momentum into the hole. In case of Kerr holes, it was shown by Wald that dangerously are simply not captured hole, and thus event horizon is destroyed. Here, we reconsider this gedanken experiment for variety geometries, from holes in higher dimensions rings. We show particular way destroying does succeed cosmic censorship preserved.
We analyze the gravitational perturbations induced by particles falling into a three dimensional, asymptotically AdS black hole geometry. More specifically, we solve linearized perturbation equations obtained from geodesic motion of ringlike distribution test in BTZ background. This setup ensures that $U(1)$ symmetry background is preserved. The nonasymptotic flatness raises difficulties attributing significance energy and angular momentum to conserved quantities particles. issue well known...
We investigate the consequences of throwing point particles into odd-dimensional Myers-Perry black holes in asymptotically anti--de Sitter (AdS) backgrounds. restrict our attention to case which angular momenta background geometry are all equal. This process allows us test generalization weak cosmic censorship conjecture AdS spacetimes higher dimensions. find no evidence for overspinning $D=5,7,9$ and 11 Instead, carrying maximum possible momentum that still fall an extremal rotating hole...
The properties of string networks at scales well below the horizon are poorly understood, but they enter critically into many observables. We argue that in some regimes, stretching will be only relevant process governing evolution. In this case, two-point function is determined up to normalization: fractal dimension approaches one short distance, rate approach characterized by an exponent plays essential role network properties. smoothness distance implies, for example, cosmic lensing images...
We use our model of the small scale structure on cosmic strings to develop further result Siemens, Olum, and Vilenkin that gravitational radiation length is smaller than previously assumed $\ensuremath{\Gamma}G\ensuremath{\mu}t$. discuss some properties string loops at this cutoff scale, we argue recent network simulations point two populations loops, one near horizon cutoff.
We compute the greybody factors for nonminimally coupled scalar fields in four-dimensional Schwarzschild--de Sitter spacetime. In particular, we demonstrate that zero-angular-momentum factor generically tends to zero zero-frequency limit like frequency squared if there is nonvanishing coupling curvature. This contrast with minimally case, where this known tend a finite constant. also study Hawking radiation massless spacetime, formulate sensible notion of generalized absorption cross section...
We extend our earlier model of the small-scale structure cosmic string networks through an improved treatment separation long and short scales. find that production small loops (at gravitational radiation scale) is a robust feature networks, in addition to population near horizon scale. obtain quantitative agreement with scaling loop functions as found simulations by two groups.
We perform a thorough study of greybody factors for minimally-coupled scalar fields propagating on the background rotating black holes in higher (odd) dimensions with all angular momenta set equal. For this special case, solution enjoys an enhanced symmetry, which translates into advantageous feature being cohomogeneity-1, i.e., these backgrounds depend single radial coordinate. Our analysis contemplates three distinct situations, cosmological constant zero, positive or negative. Using...
A bstract Tests of the weak cosmic censorship conjecture examine possibility breakdown predictivity gravitational theory considered, by checking if curvature singularities typically present in black hole spacetimes are concealed within an event horizon at all times. possible method to perform such tests was proposed Wald and consists trying overspin extremal rotating throwing it a test particle with large angular momentum. In this paper, we analyze effects dropping into quantum BTZ hole,...
We explore the integrability of five-dimensional minimal supergravity in presence three commuting Killing vectors. argue that to see structure theory one necessarily has perform an Ehlers reduction two dimensions. A direct dimensional dimensions does not allow us easy way. This situation is contrast with vacuum gravity. derive Belinski-Zakharov (BZ) Lax pair for based on a symmetric 7x7 coset representative matrix G2/(SL(2,R) x SL(2,R)). elucidate relationship between our BZ and group...
Black holes are the simplest objects in universe. They correspond to extreme deformations of spacetime geometry, and can exist even devoid matter. In general relativity, (electro)vacuum black uniquely determined by their mass, charge angular momentum. This feature follows from a uniqueness theorem, which be evaded if one considers higher dimensions or matter fields coupled gravity. Here we find that Einsteinian cubic gravity, well-motivated modification Einstein gravity includes third-order...
We construct exact solutions describing the motion of rotating thin shells in a fully backreacted five-dimensional black hole spacetime. The radial equation follows from Darmois-Israel junction conditions, where both interior and exterior geometries are taken to be equal angular momenta Myers-Perry solutions. show that rotation generates anisotropic pressures momentum along shell. Gravitational collapse scenarios including analyzed new class stationary is introduced. Energy conditions for...
We study continuously self-similar solutions of four-dimensional Einstein-Maxwell-dilaton theory, with an arbitrary dilaton coupling. Self-similarity is emergent symmetry gravitational collapse near the threshold black hole formation. The resulting ``critical collapse'' picture has been intensively studied in past for self-gravitating scalar fields or perfect fluids, but little known concerning other systems. Here, we assess impact gauge on critical collapse, context low-energy string...
The equation governing the time evolution of number density loops in a cosmic string network is detailed balance determined by energy conservation. We solve this with inclusion gravitational radiation effect, which causes to shrink (and eventually decay) as elapses. solution approaches scaling regime total remains finite, converging both infrared and ultraviolet.
We investigate the thermodynamic equilibrium states of a rotating thin shell, i.e., ring, in (2+1)-dimensional spacetime with negative cosmological constant. The inner and outer regions respect to shell are given by vacuum anti-de Sitter Ba\~{n}ados-Teitelbom-Zanelli spacetimes, respectively. first law thermodynamics on together three equations state for pressure, local inverse temperature angular velocity yields entropy which is shown depend only its gravitational radii. When pushed own...
We study gravitational perturbations sourced by a rotating test shell collapsing into five-dimensional Myers-Perry black holes in anti-de Sitter (AdS). Our attention is restricted to the case which two possible angular momenta of geometry are set equal. In this situation background cohomogeneity-1, amounts crucial technical simplification. It found that linearized Einstein equations consistent only when corotating with spacetime. However, it argued consequence matter on being described dust...