Searcharxiv⌕ Search

arXiv subjects

Muhammad Fitrah Alfian Rangga Sakti

Publications and source records attributed to Muhammad Fitrah Alfian Rangga Sakti.

12 recordsLinked to original sources
arXiv2026

Entropy Quantization and Quasi-normal Modes of Dyonic Kerr-Sen Black Holes

We explore the properties of inner and outer horizon thermodynamics of dyonic Kerr-Sen black hole (DKSBH). It is observed that the entropy (or area) product is universal, depending only on the angular momentum of the BH. We then proceed to study the dual conformal field theory~(CFT) in the Kerr/CFT correspondence using thermodynamic relations and compute the central charges from 2D CFT. The central charges are found to be universal with only angular momentum dependence. By comparing to Kerr-Newman BH, it is found that the essential difference is in the right-moving sector of the CFT. Interestingly, we can then explicitly produce the non-vanishing central charges related to its static solution, the dyonic dilaton BH, using the thermodynamic method. Moreover, from the CFT relations to multi-horizon thermodynamics, we find the analytical expression of the quasi-normal modes~(QNM) spectra in terms of BH parameters. This QNM computation supports the Bekenstein-Hod conjecture on the BH's entropy quantization.

hep-th↗
arXiv2026

Holographic Thermodynamics of Dyonic Dilaton AdS Black Holes

We investigate the holographic dual of the extended bulk thermodynamics of dyonic dilaton AdS black holes by allowing both the cosmological constant and Newton's gravitational constant to vary. In the dual CFT thermodynamics, the central charge $C$ and chemical potential $μ$ as its conjugate enter the thermodynamic relations, in addition to $(\tilde{T},\tilde{S})$, $(\tilde{Q},\tildeΦ)$, $(\tilde{P},\tildeΨ)$, $(\tilde{\mathcal{P}},\tilde{V})$. We consider sixteen different ensembles related to those five pairs of thermodynamic variables which we separate into fixed volume and pressure ensembles. Due to the symmetry on ($\tilde{Q},\tilde{P}$), we only need to analyze five ensembles each in fixed volume and pressure ensembles. In the fixed volume ensembles, it is found that the fixed ($\tilde{Q},\tilde{P},\tilde{V},μ$) and ($\tildeΦ,\tilde{P},\tilde{V},μ$) exhibit a zeroth-order phase transition. Interestingly, the fixed ($\tildeΦ,\tildeΨ,\tilde{V},C$) ensemble shows the zeroth- and first-order phase transitions at above and below critical potential $\tildeΥ_c$, respectively. In the fixed pressure ensembles, it is found that richer structures appear where the sign of $μ$ heavily influences phase space for several ensembles. For fixed ($\tilde{Q},\tilde{P},\tilde{\mathcal{P}},μ$) and ($\tildeΦ,\tilde{P},\tilde{\mathcal{P}},μ$), they show the zeroth-, first-, and second-order phase transitions. For the fixed ($\tildeΦ,\tildeΨ,\tilde{\mathcal{P}},μ$) ensemble, there is only a zeroth-order phase transition occurs. The other ensembles which we do not mention eventually do not show any phase transition. These findings provide deeper insight into how bulk gravitational variations, particularly regarding the cosmological and gravitational constants, translate to exact critical phenomena and richer phase structures within CFT.

hep-th↗
arXiv2025

Graviton Condensate Stars and Its Gravitational Echoes

We construct the exact stellar configurations that contain an ordinary perfect-fluid matter that interacts minimally with a condensate of gravitons with distinct pressure conditions on the surface. We propose vanishing transverse pressure on the surface for, namely graviton condensate type 1 and vanishing radial pressure on the surface for type 2. The condition for the radial pressure of type 1 requires the existence of a thin shell that will balance the pressure discontinuity while for type 2, the discontinuity on transverse pressure does not require the additional thin shell. It is found that the Buchdahl inequality of the resulting stellar configurations depends on the parameter related to the graviton condensate, such that we can find the ultra-compact regime of the stellar models. Moreover, the echo time and echo frequency within the ultra-compact regime are computed. At the same compactness, it is found that the presence of the graviton condensate will delay the gravitational echoes for type 2 and will expedite the gravitational echoes for type 1 compared to constant density star, $τ_{echo2}>τ_{CDS}>τ_{echo1}$. Furthermore, the gravitational perturbation of a massless scalar wave is also investigated to support these results. These results could open more opportunities for the observational study of graviton in the near future, mostly from the compact astrophysical objects.

gr-qc↗
arXiv2024

Dual CFT on Nariai limit for Kerr-Sen-dS black holes

In this work, we study the Kerr-Sen-de Sitter black hole~(BH) in the Nariai limit where the event and cosmological horizon coincide. We show that the near-horizon Kerr-Sen-de Sitter black hole in Nariai limit is a fiber over AdS$_2$ with an appropriate coordinate transformation, instead of fiber over dS$_2$. Hence, we can compute the associated central charge and CFT temperature by using the Kerr/CFT method. It is remarkably exhibited that through Cardy's growth of states, the Bekenstein-Hawking entropy on cosmological horizon is reproduced. Moreover, we show that the radial equation of the quantum scalar field in $J$- and $Q$-pictures on this charged rotating background in Nariai limit can be portrayed in quadratic Casimir operator form with $SL(2,R)\times SL(2,R)$ isometry. We also compute the corresponding thermodynamic quantities from CFT to find the absorption cross-section and real-time correlator in $J$-picture. In $Q$-picture, we do not find a well-defined CFT description. We then extend the study of quantum scalar field in Nariai limit for Kerr-Newman-dS black hole solution and show that the hidden conformal symmetry on this black hole's background in in $J$- and $Q$-pictures is well-defined.

hep-th↗
arXiv2023

Hidden conformal symmetry for dyonic Kerr-Sen black hole and its gauged family

Motivated by advanced progress in the holographic theory between rotating black holes and CFT, we explore the conformal invariance on dyonic Kerr-Sen black hole and its gauged family. We consider a neutral massless scalar probe on the black holes' background within the low-frequency limit and exhibit that the solution space possesses $SL(2,R)\times SL(2,R)$ isometry. The periodic identification of the azimuthal angle corresponds to the spontaneous conformal symmetry breaking by temperatures $T_L,T_R$. Using the computation of the central charges on Ref. [25] that we recalculate by considering the contributions of all associated fields, we successfully derive the Bekenstein-Hawking entropy from Cardy entropy formula. Furthermore, we also calculate the absorption cross-section from gravity side for generic non-extremal dyonic Kerr-Sen black hole and near-extremal gauged dyonic Kerr-Sen black hole. Our calculations show that those quantities are in a perfect match with the calculation from CFT. Therefore, our findings further support the duality between rotating black holes and CFTs.

hep-th↗
arXiv2022

Dual CFT on Dyonic Kerr-Sen black hole and its gauged and ultraspinning counterparts

We demonstrate that rotating dyonic black holes in Einstein-Maxwell-Dilaton-Axion (EMDA) theory is holographically dual with 2D conformal field theory. We first investigate the duality on dyonic Kerr-Sen black hole with non-vanishing dilaton and axion charges. The near-horizon geometry of extremal dyonic Kerr-Sen spacetime possesses the $SL(2,R) \times U (1)$ isometry allowing to employ the asymptotic symmetry group method to find the corresponding central charge. We find two different branches of the mass which correspond to CFT with two different central charges $c_L=12am_+$ and $c_L=12am_-$. The exact agreement between the Bekenstain-Hawking entropy and entropy from CFT is then found also in two different branches of extremal entropy. Furthermore, we demonstrate that this duality is robust insofar for non-zero AdS length. We show that the duality holds for both dyonic Kerr-Sen-AdS black hole and its ultraspinning counterpart. In both cases, we obtain the expected entropy from CFT which matches exactly with the Bekenstein-Hawking entropy. Since dyonic and axion charges are proportional to $1/m$, we note that there are possibly more than two branches of the central charge for non-zero AdS length in terms of mass. When we turn off dyonic charge, the axion charge vanishes showing the results of Kerr-Sen-AdS black hole. Moreover, when we assume the equal electromagnetic charges, it recovers the results when the dilaton charge vanishes. In the end, we compare the results of dyonic Kerr-Sen-AdS black hole and its ultraspinning counterpart to those of the dyonic Kerr-Newman-AdS black hole and the ultraspinning counterpart. Depending on the dyonic charge parameters, it is found that extremal ultraspinning dyonic Kerr-Sen-AdS black hole is not always superentropic.

hep-th↗
arXiv2022

Rotating black holes and exotic compact objects in the Kerr/CFT correspondence within Rastall gravity

Quantum gravitational effects on the near horizon may alter the black hole's horizon drastically to be partially reflective, portrayed by a quantum membrane. With this modification, the object can be considered as an exotic compact object (ECO). Quantum effects on the strong gravitational regime may also lead to a non-conserved matter tensor that can be described phenomenologically using Rastall gravity. In this work, we study the properties of black holes and ECOs within Rastall gravity using Kerr/CFT correspondence. We systematically investigate the properties of the most general rotating black hole solutions in Rastall gravity, i.e., Kerr-Newman-NUT-Kiselev, and reveal its hidden conformal symmetry. The Cardy microscopic entropy formula and absorption cross-sections from 2D CFT are computed and then matched with gravity calculation. We also extend the dual CFT analysis for studying the properties of ECOs. The existence of the quantum membrane leads to the appearance of the gravitational echoes that is manifested as an oscillatory feature on the absorption cross-section. We compute the absorption cross-section and quasi-normal modes in the dual CFT picture. We also compare the absorption cross-section of ECOs to that of black holes. We find that the Rastall coupling constant plays a significant role for both objects. We also obtain that the echo time delay depends explicitly on the Rastall coupling constant. This coupling constant may play a role to recover the correction on time delay that is believed as a non-linear physics effect. Henceforth, the signature of the Rastall gravity can be probed from the time-delay observation.

hep-th↗
arXiv2021

Dark Energy Stars with Phantom Field

Dark energy is the constituent with an enormous abundance of the present universe, responsible for the universe's accelerated expansion. Therefore, it is plausible that dark energy may interact within any compact astrophysical objects. The author in Ref. [Phys. Rev. D 83, 127501 (2011)], constructs an exact star solution consisting of an ordinary matter and phantom field from a constant density star (CDS) known as Schwarzschild interior solution. The star denotes a dark energy star (DES). The author claims that the phantom field represents dark energy within the star. So far, the role of the phantom field as dark energy in DES is not systematically studied yet. Related to this issue, we analyze the energy condition of DES. We expect that DES shall violate the strong energy condition (SEC) for a particular condition. We discover that SEC is fully violated only when the compactness reaches the Buchdahl limit. Furthermore, we also investigate the causal conditions and stabilities due to the convective motion and gravitational cracking. We also find that those conditions are violated. These results indicate that DES is not physically stable. However, we may consider DES as an ultra-compact object of which we can calculate the gravitational wave echo time and echo frequency and compare them to those of CDS. We find that the contribution of the phantom field delays the gravitational wave echoes. The effective potential of the perturbed DES is also studied. The potential also enjoys a potential well like CDS but with a deeper well. We also investigate the possibility that DES could form a gravastar when $ C=1 $. It is found that gravastar produced from DES possesses no singularity with a dS-like phase as the interior. These results could open more opportunities for the observational study of dark energy in the near future, mostly from the compact astrophysical objects.

gr-qc↗
arXiv2021

CFT Duals on Rotating Charged Black Holes Surrounded by Quintessence

We demonstrate that Kerr/CFT duality can be extended to rotating charged black hole solution surrounded by quintessence in Rastall gravity. Since Rastall gravity can be considered as $F(R,T) = R + βT $ theory with the addition of a matter term, so the gravitational Lagrangian is resemblant to Einstein general relativity. In fact, the resulting central term is coincident to the central term in the general relativity since $ T $ is only a trace of the matter term. We then exhibit that the entropy from CFT of this black hole is equivalent with the Bekenstein-Hawking entropy with no correction related to the Rastall coupling constant. Moreover, when Rastall coupling constant $ κλ$ is switched off and $ a $ is approaching zero, we may extend the solution to the 5D black hole solution. It is found that this extremal solution contains twofold CFT duals that we call as $Q$-picture and $ P $-picture. In both pictures, the CFT entropy reproduces exactly the Bekenstein-Hawking entropy for Reissner-Nordström black hole surrounded by quintessence. The results establish that, for all black holes surrounded by quintessence, the microscopic entropies of the dual CFTs agree with the Bekenstein-Hawking entropies.

hep-th↗
arXiv2019

Kerr/CFT Correspondence on Kerr-Newman-NUT-Quintessence Black Hole

Rotating black hole solution surrounded by quintessential matter is recently discussed because it might be the promising solution to study the effect of dark energy in small scale of the universe. This quintessential solution is originally derived from the condition of additivity and linearity for the energy-momentum tensor. We carry out the thermodynamic properties of this solution using the Kerr/CFT correspondence for several specific quintessential equation of state parameters. A problem arises when we compute the central charge because the canonical conserved charge is needed to be calculated from the Lagrangian. However, the exact Lagrangian of the quintessence is not defined yet in the original derivation. Yet we solve this problem by the assumption that there is only a contribution from gravitational field to the central charge. Then we could find the entropy of this black hole after calculating the temperature and using Cardy entropy formula. Another problem comes out when the spin goes to zero to find the Reissner-Nordström-NUT-Quintessence solution. To solve it, we extend to the 5-dimensional solution. In the end, we obtain the entropy for this 5-dimensional solution. So the quintessential black hole solution is dual with the CFT.

hep-th↗
arXiv2019

CFT duals on extremal rotating NUT black hole

We investigate the Kerr-Newman-NUT black hole solution obtained from Plebański-Demiański solutions with several assumptions. The origin of the microscopic entropy of this black hole is investigated using the conjectured Kerr/CFT correspondence which is originally proposed for extremal Kerr black holes. The isometry of the near-horizon extremal Kerr-Newman-NUT black hole shows that the asymptotic symmetry group may be implemented to compute the central charge of the Virasoro algebra. Furthermore, by assuming Frolov-Thorne vacuum, the conformal temperatures can be obtained. Then by using the Cardy formula, the microscopic entropy is gained which matches the Bekenstein-Hawking entropy. We also employ Cardy prescription to find the logarithmic correction of the entropy. Then at limit $ a \rightarrow 0 $, the extremal Reissner-Nordström-NUT solution is recovered and by enhancing with the fibered coordinate we find the five-dimensional (5D) solution. The second dual CFT is applied to this black hole to gain the entropy. Finally, the microscopic entropy is still in agreement with the area law of 5D black hole solution. Hence, the extremal Reissner-Nordström-NUT solution is holographically dual to the CFT.

hep-th↗