Browsing by Author "Düztaş, Koray"

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Citation Count: 0
Can the induced increase in the angular velocity prevent the overspinning of BTZ black holes?
(Springer, 2024) Duztas, Koray; Düztaş, Koray
Previously we showed that nearly extremal Ba & ntilde;ados-Teitelboim-Zanelli (BTZ) black holes can be overspun by test bodies and fields, following the work of Rocha and Cardoso for the extremal case. The naked singularities in AdS space-times correspond to states rotating faster than light in the Ads/CFT correspondence. Therefore, overspinning turns out to be a drastic problem in a (2 + 1) dimensional AdS space-time, where one cannot invoke backreaction effects. Here, we consider the induced increase in the angular velocity of the event horizon which modifies the condition to allow the absorption of the perturbations satisfying the null energy condition. We show that its magnitude is sufficiently large to prevent the absorption of the challenging modes both for test bodies and scalar fields. We bring a solution to the notorious overspinning problem which does not involve any reference to self-energy or gravitational radiation
Citation Count: 0
Challenging event horizons with spin (3/2) fields
(Springer, 2023) Duztas, Koray; Düztaş, Koray
We attempt to destroy the event horizons of Kerr black holes by perturbing them with massless spin (3/2) fields. We carry out a detailed analysis by incorporating the explicit form of the absorption probabilities and backreaction effects due to the self energy of the test fields. For extremal and nearly extremal black holes, backreaction effects dominate for perturbations with large magnitudes. However, small perturbations can destroy the event horizons of extremal black holes and drive nearly extremal black holes closer to extremality. Eventually, nearly extremal black holes reach a certain stage where they can be continuously driven to extremality and beyond. Both the cosmic censorship conjecture and the third law of black hole dynamics can be violated by spin (3/2) fields. This directly follows from the fact that fermionic fields do not satisfy the null energy condition. Therefore this result does not contradict with the fact that cosmic censorship and the laws of black hole mechanics remain valid for perturbations satisfying the null energy condition.
Citation Count: 0
Spin-2 fields and cosmic censorship
(Amer Physical Soc, 2024) Duztas, Koray; Düztaş, Koray
We evaluate the possibility of the formation of naked singularities in the interaction of Kerr black holes with test massless spin-2 fields. We analyze the scattering problem for both extremal and nearly extremal black holes by incorporating the explicit form of the absorption probabilities. We show that extremal black holes become nonextremal after the interaction with the modes with both positive and negative absorption probabilities. For nearly extremal black holes the absorption probability for the challenging modes turns out to be of the order & varepsilon;5, where & varepsilon; parametrizes the closeness to extremality. Though the highest absorption probability for m 1/4 2 modes pertains to spin-2 fields, its drastically small value implies that the event horizon is preserved without the need to employ the backreaction effects. The result can be qualitatively extrapolated to hypothetical higher integer spin fields. We also review and extend our previous comments on Sorce-Wald method. We show that the order magnitude problems can be avoided by abandoning the nonphysical parameter 2. The conditions derived by Sorce-Wald can be legitimately used to incorporate the backreaction effects by avoiding to multiply them by 22, thereby preserving the magnitude of their contribution. We apply this method to the problems of overcharging Reissner-Nordstr & ouml;m black holes and overspinning Kerr black holes, in a rough analysis ignoring absorption probabilities which could apply to test bodies.