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Register a new userViolations of Weak Cosmic Censorship in Black Hole collisions
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We study collisions of boosted rotating black holes in $D=6$ and 7 spacetime dimensions with a non-zero impact parameter. We find that there exists an open set of initial conditions such that the intermediate state of the collision is a dumbbell-like horizon which is unstable to a Gregory-Laflamme-type instability. As is usually the case for similar unstable configurations, the evolution of such an instability leads to a pinch off of the horizon in finite asymptotic time, thus forming a naked singularity. Hence, this is the first fully genuine violation of Weak Cosmic Censorship conjecture in higher dimensional asymptotically flat spacetimes.
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We study the evolution of black hole collisions and ultraspinning black hole instabilities in higher dimensions. These processes can be efficiently solved numerically in an effective theory in the limit of large number of dimensions D. We present evidence that they lead to violations of cosmic censorship. The post-merger evolution of the collision of two black holes with total angular momentum above a certain value is governed by the properties of a resonance-like intermediate state: a long-lived, rotating black bar, which pinches off towards a naked singularity due to an instability akin to that of black strings. We compute the radiative loss of spin for a rotating bar using the quadrupole formula at finite D, and argue that at large enough D ---very likely for $Dgtrsim 8$, but possibly down to D=6--- the spin-down is too inefficient to quench this instability. We also study the instabilities of ultraspinning black holes by solving numerically the time evolution of axisymmetric and non-axisymmetric perturbations. We demonstrate the development of transient black rings in the former case, and of multi-pronged horizons in the latter, which then proceed to pinch and, arguably, fragment into smaller black holes.
We produce the first concrete evidence that violation of the weak cosmic censorship conjecture can occur in asymptotically flat spaces of five dimensions by numerically evolving perturbed black rings. For certain thin rings, we identify a new, elastic-type instability dominating the evolution, causing the system to settle to a spherical black hole. However, for sufficiently thin rings the Gregory-Laflamme mode is dominant, and the instability unfolds similarly to that of black strings, where the horizon develops a structure of bulges connected by necks which become ever thinner over time.
Based on the new version of the gedanken experiment proposed by Sorce and Wald, we investigate the weak cosmic censorship conjecture (WCCC) for a Reissner-Nordstr{o}m-Anti-de Sitter (RN-AdS) black hole under the perturbation of extra matter fields. Firstly, we propose that the cosmological constant can be effectively derived from the matter fields and its value varies with the matter fields perturbing the black hole. Meanwhile, we assume that the perturbation satisfies the stability condition. This condition means that after a long time of the perturbation, the black hole solution also belongs to the family of the RN-AdS solution. After that, based on both the stability condition and the null energy condition, while using the off-shell variation method, the first-order and the second-order perturbation inequalities are derived respectively when the cosmological constant is considered as a dynamic variable. It is the first time to extend the two perturbation inequalities to contain the term of the press and volume of thermodynamics. Finally, we perform the two perturbation inequalities into testing the WCCC for the RN-AdS black hole under the second-order approximation of the perturbation. It is shown that if the variation of the cosmological constant is caused by the matter fields, while the stability condition and the null energy condition are all satisfied, the black hole cannot be destroyed after the perturbation. In other words, the WCCC for the RN-AdS black hole is valid under the second-order approximation of the perturbation.
We investigate extremal electrically charged black holes in Einstein-Maxwell-dilaton theory with a cosmological constant inspired by string theory. These solutions are not static, and a timelike singularity eventually appears which is not surrounded by an event horizon. This suggests that cosmic censorship may be violated in this theory.
We study the model of Einstein-Maxwell theory minimally coupling to a massive charged self-interacting scalar field, parameterized by the quartic and hexic coupling, labelled by $lambda$ and $beta$, respectively. In the absence of scalar field, there is a class of counterexamples to cosmic censorship. Moveover, we investigate the properties of full nonlinear solution with nonzero scalar field, and argue that, by assuming massive charged self-interacting scalar field with sufficiently large charge above one certain bound, these counterexamples can be removed. In particular, this bound on charge for self-interacting scalar field is no longer equal to the weak gravity bound for free scalar case. In the quartic case, the bounds are below free scalar case for $lambda<0$, while above free scalar case for $lambda>0$. Meanwhile, in the hexic case, the bounds are above free scalar case for both $beta>0$ and $beta<0$.
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