arXiv subjects

Haryanto M. Siahaan

Publications and source records attributed to Haryanto M. Siahaan.

At least 37 records · Page 2Linked to original sources

arXiv2021

Destroying Kaluza-Klein and Kerr-Newman black holes

We investigate the destroying of charged and rotating black holes in Einstein-Maxwell-(dilaton) theory. We show that a test particle with some appropriate properties in the black hole background can turn the black hole into a naked singularity. In this work, we neglect the self-force, self-energy, and radiative effects as considered by some others in literature. As the result, we are able to show that the Kerr-Newman and Kaluza-Klein black holes can be destroyed by the test particle. Furthermore, for Kaluza-Klein black hole, we consider the overspinning of the black hole by a neutral test scalar field.

gr-qc↗

arXiv2021

Magnetized Kerr-Newman-Taub-NUT spacetimes

We find a new class of exact solutions in the Einstein-Maxwell theory by employing the Ernst magnetization process to the Kerr-Newman-Taub-NUT spacetimes. We study the solutions and find that they are regular everywhere. We also find the quasilocal conserved quantities for the spacetimes, the corresponding Smarr formula and the first law of thermodynamics.

gr-qc↗

arXiv2021

Magnetized Reissner-Nordstrom-Taub-NUT spacetime and microscopic entropy

We present a novel solution describing magnetized spacetime outside a massive object with electric charge equipped with NUT parameter. To get the solution, we employ the Ernst magnetization to the Reissner-Nordstrom-Taub-NUT spacetime as the seed. After discussing some physical aspects of the spacetime, we show that the extremal entropy of a magnetized Reissner-Nordstrom-Taub-NUT black hole can be reproduced by using the Cardy formula.

gr-qc↗

arXiv2021

Magnetized Kerr-Taub-NUT spacetime and Kerr/CFT correspondence

We present a new solution in Einstein-Maxwell theory which can be considered as the magnetized version of Kerr-Taub-NUT solution. Some properties of the spacetime are discussed. We also compute the entropy of extremal black hole in the spacetime by using the Kerr/CFT correspondence approach.

gr-qc↗

arXiv2020

Rotating and charged Taub-NUT-(A)dS spacetimes on a 3-brane

We construct novel solutions to the effective Einstein equation with four dimensional cosmological constant on a 3-brane in Randall-Sundrum II scenario. The charged solution is obtained by assuming the existence of localized Maxwell fields on the 3-brane. Timelike and null circular geodesics in the neutral rotating braneworld spacetime with NUT parameter are discussed, and we find that such geodesics cannot occur on the equatorial plane. On non-equatorial planes, timelike circular geodesics can occur for the negative tidal charge, but we cannot find numerical results to support the existence of non-equatorial null circular geodesics.

gr-qc↗

arXiv2020

Kerr-Sen-Taub-NUT spacetime and circular geodesics

We present a novel solution obeying classical equation of motion in the low energy limit of heterotic string theory. The solution represents a rotating mass with electric charge and gravitomagnetic monopole moment. The corresponding conserved charges are discussed. We also study the test body circular equatorial motions in the spacetime.

gr-qc↗

arXiv2020

Merger estimates for Kerr-Sen black holes

The advent of gravitational wave observation starts a new era of precision tests of gravitational theory. Estimations of black holes mergers should come from any well established gravitational theories, provided that the theory has not been ruled out by observations. In this paper we consider the low energy limit of heterotic string theory where the associated rotating and charged black holes are described by the Kerr-Sen solution. We investigate the approximate final spins and quasinormal modes of the black hole resulting from the merger process.

gr-qc↗

arXiv2020

Pair production of scalars around near-extremal Kerr-Sen black holes

We investigate the charged scalar pair production near the horizon of a near-extremal Kerr-Sen black holes. The condition for pair production to occur has relation to the violation of Breitenlohner-Freedman bound in an AdS$_2$ space. The method employed in this work has been used to show the pair production in the near-horizon of a near-extremal Kerr-Newman black hole and its non-rotating case as well. We also discuss the static limit of our result.

gr-qc↗

arXiv2018

Accelerating black holes in the low energy heterotic string theory

We present a new solution describing a pair of rotating, charged, and accelerating black holes in in the low energy limit of heterotic string theory. To obtain the solution, we apply the Hassan-Sen transformation to the neutral accelerating Kerr spacetime as the seed solution. Some properties of the black hole solutions are discussed.

hep-th↗

arXiv2018

Hidden conformal symmetry for the accelerating Kerr black holes

According to Kerr/CFT correspondence, some aspects of extremal and non-extremal Kerr black holes could be explained by using a 2D CFT. This paper is devoted to show how Kerr/CFT correspondence can work for the slowly accelerating Kerr black holes, in both extremal and non-extremal cases. The equation of motion for low frequency scalar probes in the near region possesses the "hidden" conformal symmetry, similar to that of the non-accelerating version. Assuming a particular value of associated central charge, Cardy formula in 2D CFT can recover the Bekenstein-Hawking entropy for the black hole under consideration. Moreover, agreements in the scattering process between gravitational and 2D CFT dual suggest the existence of slowly accelerating Kerr/CFT duality.

gr-qc↗

arXiv2017

Destroying extremal magnetized black holes

The gedanken experiment by Wald to destroy a black hole using a test particle in the equatorial plane is adopted to the case of extremal magnetized black holes. We find the presence of external magnetic fields resulting from the "Ernst magnetization" permits a test particle to have strong enough energy to destroy the black hole. However, the corresponding effective potentials show that such particles would never reach the horizon.

gr-qc↗

arXiv2016

Magnetized Kerr/CFT Correspondence

We extend the conjectured Kerr/CFT correspondence to the case of extremal Kerr black holes immersed by an magnetic field, namely the extremal Melvin-Kerr black holes. We compute the central charge which appears in the associated Virasoro algebra generated by a class of diffeomorphisms that satisfies a set of boundary conditions in the near horizon of an extremal Melvin-Kerr black hole. Our results support the Kerr/CFT conjecture, where the macroscopic Bekenstein-Hawking entropy for an extremal Melvin-Kerr black hole matches the result obtained from a dual 2D CFT microscopic computation using Cardy formula. Interestingly, the dual CFT description could be non-unitary, due to the possibility of negative central charge.

hep-th↗

arXiv2016

Destroying Kerr-Sen black holes

By neglecting the self-force, self-energy, and radiative effects, it has been shown that an extremal or near-extremal Kerr-Newman black hole can turn into a naked singularity when it captures charged and spinning massive particles. A straightforward question then arises: do charged and rotating black holes in string theory possess the same property? In this paper we apply the Wald's gedanken experiment, in his study on the possibility of destroying extremal Kerr-Newman black holes, to the case of (near-)extremal Kerr-Sen black holes. We find that feeding a test particle into a (near-)extremal Kerr-Sen black hole could lead to a violation of the extremal bound for the black hole.

gr-qc↗

arXiv2016

Higher Spins Tunneling from a Time Dependent and Spherically Symmetric Black Hole

The discussions of Hawking radiation via tunneling method have been performed extensively in the case of scalar particles. Moreover, there are also several works in discussing the tunneling method for Hawking radiation by using higher spins, e.g. neutrino, photon, and gravitino, in the background of static black holes. Interestingly, it is found that the Hawking temperature for static black holes using the higher spins particles has no difference compared to the one computed using scalars. In this paper, we study the Hawking radiation for a spherically symmetric and time dependent black holes using the tunneling of Dirac particles, photon, and gravitino. We find that the obtained Hawking temperature is similar to the one derived in the tunneling method by using scalars.

gr-qc↗

arXiv2015

Instability of charged massive scalar fields in bound states around Kerr-Sen black holes

We show the instability of a charged massive scalar field in bound states around Kerr-Sen black holes. By matching the near and far region solutions of the radial part in the corresponding Klein-Gordon equation, one can show that the frequency of bound state scalar fields contains an imaginary component which gives rise to an amplification factor for the fields. Hence, the unstable modes for a charged and massive scalar perturbation in Kerr-Sen background can be shown.

hep-th↗

arXiv2011

On non-relativistic $Q\bar Q$ potential via Wilson loop in Galilean space-time

We calculate the static Wilson loop from string/gauge correspondence to obtain the $Q\bar Q$ potential in non-relativistic quantum field theory, i.e. CFT with Galilean symmetry. We analyze the convexity conditions \cite{bachas} for $Q\bar Q$ potential in this theory, and obtain restrictions for the acceptable dynamical exponent $z$.

hep-th↗

arXiv2011

Semiclassical Methods for Hawking Radiation from a Vaidya Black Hole

We derive the general form of Hawking temperature for Vaidya black hole in the tunneling pictures. This kind of black hole is regarded as the description of a more realistic one since it's time dependent decreasing mass due to the evaporation process. Clearly, the temperature would be time dependent as our findings. We use the semiclassical methods, namely radial null geodesic and complex paths methods. Both methods are found to give the same results. Then, we discuss the possible form of corresponding entropy.

gr-qc↗

arXiv2009

On Hawking Radiation as Tunneling Phenomenon with Dissipation Effect

In this letter, we derive the Hawking temperature in the tunneling method by considering the system is open to the environment. This consideration yields the temperature which is higher than the standard one. The correction of temperatures depends on spectral density of bath oscillators which is responsible for dissipation effect in our analysis.

gr-qc↗