arXiv subjects

H. Hadi

Publications and source records attributed to H. Hadi.

18 recordsLinked to original sources

arXiv2026

High-Frequency Gravitational-Wave Transduction in a SQUID-Terminated Superconducting Cavity

High-frequency gravitational waves in the MHz--GHz range require detection strategies beyond conventional interferometers. We study the response of a SQUID-terminated superconducting microwave cavity as a narrowband parametric transducer. The cavity boundary conditions and the flux dependence of the Josephson inductance are used to derive the quarter-wave mode spectrum and the first-order eigenfrequency response to changes in the physical line length, phase velocity, and SQUID inductive length. By projecting the perturbed dynamics onto the static cavity modes, we show that the resonance-frequency response and the photon-pair-production response are generally distinct. We therefore introduce two independent kernels, $R_n^{\omega}$ and $R_n^{\rm pair}$, which coincide only when changes in mode normalization and spatial profiles can be neglected. Near $\Omega_{\rm GW}\simeq 2\omega_n$, the isolated-mode dynamics reduce to a Mathieu-type parametric amplifier, allowing the photon number, quadrature variances, gain, and instability threshold to be obtained in the presence of dissipation. Spontaneous photon production scales quadratically with the gravitational-wave strain and is extremely small for representative parameters, whereas phase-sensitive responses with a coherent probe can scale linearly with strain. The framework therefore provides a theoretical description of narrowband gravitational-wave transduction, while a quantitative sensitivity estimate requires device-specific calibration of the mechanical--electromagnetic response, verification of mode isolation, and a complete treatment of loss and noise.

gr-qc↗

arXiv2025

Quantum circuit simulation of black hole evaporation and Maxwell demon interpretation

We suggest a quantum circuit model which simulates the black-hole evaporation process. In particular, Almheiri-Marolf-Polchinski-Sully (AMPS) paradox and the ER=EPR correspondence are reconsidered regarding our proposed model, which assumes a Maxwell's demon operating within a black hole interior. In other words, we form a quantum circuit, mimicking the behavior of the entanglement structure of the near-horizon region and the early Hawking radiation located far from the black hole. Furthermore, we indicate how the demon, by applying nonlocal correlations, can mediate via Einstein-Rosen bridges for the purpose of simulating the transfer of quantum information across the horizon without violating the monogamy of entanglement. Finally, the thermodynamic cost of the demon's operations regarding Landauer's principle is analyzed. This indicates that the information erasure has an energy comparable to the black hole entropy.

gr-qc↗

arXiv2024

Gravitational wave pulse and memory effects for hairy Kiselev black hole and its analogy with Bondi-Sachs formalism

The investigation of non-vacuum cosmological backgrounds containing black holes is greatly enhanced by the Kiselev solution. This solution plays a crucial role in understanding the properties of the background and its relationship with the features of the black hole. Consequently, the gravitational memory effects at large distances from the black hole offer a valuable means of obtaining information about the surrounding field parameter N and parameters related to the hair of the hairy Kiselev Black hole. This paper investigates the gravitational memory effects in the context of the Kiselev solution through two distinct approaches. At first, the gravitational memory effect at null infinity is explored by utilizing the Bondi-Sachs formalism by introducing a gravitational wave (GW) pulse to the solution. The resulting Bondi mass is then analyzed to gain further insight. Therefore, the Kiselev solution is being examined to determine the variations in Bondi mass caused by the pulse of GWs. The study of changes in Bondi mass is motivated by the fact that it is dynamic and time-dependent, and it measures mass on an asymptotically null slice or the densities of energy on celestial spheres. In the second approach, the investigation of displacement and velocity memory effects is undertaken in relation to the deviation of two neighboring geodesics and the deviation of their derivative influenced by surrounding field parameter N and the hair of hairy Kiselev black hole. This analysis is conducted within the context of a gravitational wave pulse present in the background of a hairy Kiselev black hole surrounded by a field parameter N.

gr-qc↗

arXiv2024

Gravitational memory effects of black bounces and a traversable wormhole

Black bounces are spacetimes that can be interpreted as either black holes or wormholes depending on specific parameters. In this study, we examine the Simpson-Visser and Bardeen-type solutions as black bounces and investigate the gravitational wave in the background of these solutions. We then explore the displacement and velocity memory effects by analyzing the deviation of two neighboring geodesics and their derivatives influenced by the magnetic charge parameter a. This investigation aims to trace the magnetic charge in the gravitational memory effect. Additionally, we consider another family of traversable wormhole solutions obtained from non-exotic matter sources to trace the electric charge Q_e in the gravitational memory effect, which can be determined from the far field asymptotic. Furthermore, this research aims to explore the gravitational memory effect related to the variation in Bondi mass for the Simpson-Visser and Bardeen-Type black bounces. The investigation will also be conducted on a traversable wormhole solution that does not require any exotic field. This study holds importance in not only identifying compact objects such as wormholes through gravitational memory effects but also in observing the charge Qe, which offers a tangible manifestation of Wheeler's idea of "electric charge without charge."

gr-qc↗

arXiv2024

Quantum cosmology in teleparallel gravity with a boundary term

We quantize a homogeneous and isotropic universe for two models of modified teleparallel gravity, wherein an arbitrary function of the boundary term, namely $B$, is present in the action and in the other model a scalar field that is non-minimally coupled to both the torsion and boundary term. In this regard, we study exact solutions of both the classical and quantum frameworks by utilizing the corresponding Wheeler-DeWitt (WDW) equations of the models. To correspond to the comprehensive classical and quantum levels, in the second model, we propose an appropriate initial condition for the wave packets and observe that they closely adhere to the classical trajectories and reach their peak. We quantify this correspondence using the de-Broglie Bohm interpretation of quantum mechanics. According to this proposal, the classical and Bohmian trajectories coincide when the quantum potential vanishes along the Bohmian paths. Furthermore, we apply the de-parameterization technique to our model in the realm of the problem of time in quantum cosmological models based on the WDW equation, utilizing the global internal time denoted as $\chi$, which represents a scalar field.

gr-qc↗

arXiv2023

Non-locally Reconstructed both Sides of Wormhole and its Non-Traversability

The theoretical implications of a traversable wormhole between entangled black holes are significant in terms of non-locality and superluminal signaling. By utilizing the entangled states of two maximally entangled black holes, it becomes possible to construct a wormhole. In this context, the traversable wormhole can be achieved by exciting the vacuum state of the near-horizon region of one black hole, allowing for the transmission of information to an observer situated in the near-horizon region of the other black hole through the wormhole. However, the occurrence of this phenomenon is restricted when the near-horizon regions of the black holes undergo a non-local reconstruction, which is referred to as the ER=EPR correspondence. We argue that this correspondence imposes a fundamental limitation on the potential traversability of wormhole and the occurrence of superluminal signaling.

hep-th↗

arXiv2023

Source of black bounces in Rastall gravity

In this study, we explore the black bounce solution in Rastall gravity and its potential source field, which can be described as a black hole or wormhole solution depending on certain parameters. We focus on the Bardeen-Type black bounce and Simpson-Visser solution and aim to identify an appropriate source field for these solutions. Our findings suggest that in Rastall gravity, a source for the black bounce solution with non-linear electromagnetic can be found. However, in the presence of a non-linear electromagnetic source, it is impossible to identify an appropriate source for the black bounce solution without a scalar field. We also investigate the energy conditions outside the event horizon for two types of black bounce solutions: Simpson-Visser and Bardeen. We find that these solutions do not satisfy the null energy condition, but we also reveal that Rastall gravity has more flexibility for maintaining some of the energy conditions by selecting an appropriate value for the Rastall parameter $\gamma$.

gr-qc↗

arXiv2023

Dynamical non-locality in the near-horizon region of a black hole with quantum time

The formalization of the modular energy operator within the curved spacetime is achieved through the timeless approach proposed by Page and Wootters. The investigation is motivated by the peculiar behavior of the near horizon region of a black hole and its quantum effects, leading to a restriction of the study to the immediate vicinity. The focus lies on the perspective of a static observer positioned close to the horizon. This paper highlights the alteration of the modular energy's behavior in this region compared to flat spacetime. Furthermore, it is observed that the geometry of the spacetime influences the non-local properties of the modular energy. Moreover, within the event horizon of the black hole, the modular energy exhibits a completely distinct behavior, rendering its modular behavior imperceptible in this specific region.

gr-qc↗

arXiv2022

Quantum time dilation in the near-horizon region of a black hole

In this work, we obtain a relation for average quantum time dilation between two clocks A and B in the near-horizon region of a black hole supported by the Rindler metric and conformal tortoise coordinate. It is indicated that this relation is identified with time dilation in classical and flat background limits.

gr-qc↗

arXiv2022

Quantum time in near-horizon region of a black hole

The understanding of time and dynamics can be elucidated by examining the concept of entanglement in quantum theory. This particular perspective on time is referred to as the timeless approach, which posits that the universe exists in a fixed state where two separate subsystems, namely the "clock" and the "rest," are entangled. By selecting an appropriate observable for the clock, the state of the rest of the universe evolves unitarily in relation to the variable that labels the clock observable's eigenstates, which is then interpreted as time. This intriguing model, initially introduced by Page and Wootters, has also been applied to the context of curved spacetime. In this study, we explore various uncertainties pertaining to the dynamics of the rest of the universe within a curved spacetime, including ambiguities related to the clock, the system's time evolution, the flow of time, and the recording of its history. Our investigation is primarily focused on the near horizon region of a black hole, as the peculiar behavior of quantum effects in this area allows for a thorough examination of the timeless depiction proposed by Page and Wootters in describing the system's dynamics within curved spacetime. This analysis may be valuable for quantum gravity projects that align with the approach put forth by Page and Wootters. It is worth noting that the application of the Page and Wootters approach in this particular region results in a distinct clock without any ambiguity. However, the other aforementioned issues, unlike those resolved in the realm of quantum mechanics, persist in this region.

gr-qc↗

arXiv2022

Time evolution of the inside of the black hole's horizon

We consider the Wheeler-DeWitt equation near the horizon of the black hole where the entangled vacuum state is chosen as the static universe state. Then, using the entangled property of the vacuum state, we investigate the dynamical evolution of the subsystems, namely inside and outside of the horizon.

gr-qc↗

arXiv2021

Entropic considerations on the Universe and Universe-Black Hole Systems

We study the entropic considerations on the Universe system and the Universe-Black hole system, filled by cosmological constant or exotic quintessence-like and phantom-like fields having negative pressure, using their relevant entropic bounds. It turns out that for both systems these considerations single out the cosmological constant, among the negative pressure candidate fields, as the viable cosmological field.

gr-qc↗

arXiv2020

D-bound and Bekenstein Bound for the Surrounded Vaidya Black Hole

We study the Vaidya black hole surrounded by the exotic quintessence-like, phantom-like and cosmological constant-like fields by means of entropic considerations. Explicitly, we show that for this thermodynamical system, the requirement for the identification of D-bound and Bekenstein entropy bound can be considered as a thermodynamical criterion by which one can rule out the quintessence-like and phantom-like fields, and prefer the cosmological constant as a viþable cosmological field.

gr-qc↗

arXiv2020

D-bound and Bekenstein bound for McVittie solution surrounded by dark energy cosmological fields

The cosmological candidate fields for dark energy as quintessence, phantom and cosmological constant, are studied in terms of an entropic hypothesis imposed on the McVittie solution surrounded by dark energy. We certify this hypothesis as "$D$-bound-Bekenstein bound identification" for dilute systems and use it as a criterion to determine which candidate of dark energy can satisfy this criterion for a dilute McVittie solution. It turns out that only the cosmological constant can pass this criterion successfully while the quintessence and phantom fields fail, as non-viable dark energy fields for this particular black hole solution. Moreover, assuming this black hole to possess the saturated entropy, the entropy-area law and the holographic principle can put two constraints on the radius $R$ of the cosmological horizon. The first one shows that the Hubble radius is discrete such that for any arbitrary value of the black hole mass $m_{0}$, the value of $R$ is determined up to an integer number. The latter one shows that when a black hole is immersed in a cosmological background, the radius of the cosmological horizon is constrained as $R<\frac{1}{H}$.

gr-qc↗

arXiv2019

Bousso's Covariant Entropy Bound and Padmanabhan's Emergent Universe

We study the Padmanabhan's emergent Universe in the context of Bousso's covariant entropy conjecture. We find that for a flat Universe, this conjecture can be applied for the system of Padmanabhan's emergent Universe. It turns out that the maximum "bulk entropy" of Padmanabhan's emergent Universe coincides with the upper bound of Bousso's covariant entropy on the null surface defined by Hubble horizon, provided that the Universe is just filled by the cosmological constant or radiation field which represent maximal entropy during inflation and subsequent radiation dominant era. This maximal entropy is lost by the appearance of matter system in the Universe at matter dominant era. Applying D-bound on the matter system in the Padmanabhan's emergent Universe, we find that the apparent cosmological horizon of a flat Universe in matter dominant era has less area and entropy than those (maximal) of apparent cosmological horizon of an empty de-Sitter space, in complete agreement with our conclusion. The maximal area and entropy in the Padmanabhan's emergent Universe are recovered "as soon as possible" by transition from matter dominant to cosmological constant eras, provided that the matter inside the Universe is moved completely outward the apparent cosmological horizon in "an accelerating way" at late times.

gr-qc↗

arXiv2018

Emergent Cosmos in Einstein-Cartan Theory

Based on the Padmanabhan's proposal, the accelerated expansion of the universe can be driven by the difference between the surface and bulk degrees of freedom in a region of space, described by the relation $dV/dt=N_{sur}-N_{bulk}$ where $N_{sur}$ and $N_{bulk}=-N_{em}+N_{de}$ are the degrees of freedom assigned to the surface area and the matter-energy content inside the bulk such that the indexes $"em"$ and $"de"$ represent energy-momentum and dark energy, respectively. In the present work, the dynamical effect of the Weyssenhoff perfect fluid with intrinsic spin and its corresponding spin degrees of freedom in the framework of Einstein-Cartan (EC) theory are investigated. Based on the modification of Friedmann equations due to the spin-spin interactions, a correction term for the Padmanabhan's original relation $dV/dt=N_{sur}+N_{em}-N_{de}$ including the number of degrees of freedom related to this spin interactions is obtained through the modification in $N_{bulk}$ term as $N_{bulk}=-N_{em}+N_{spin}+N_{de}$ leading to $dV /d t=N_{sur}+N_{em}-N_{spin} -N_{de}$ in which $N_{spin}$ is the corresponding degrees of freedom related to the intrinsic spin of the matter content of the universe. Moreover, the validity of the unified first law and the generalized second law of thermodynamics for the Einstein-Cartan cosmos are investigated. Finally, by considering the covariant entropy conjecture and the bound resulting from the emergent scenario, a total entropy bound is obtained. Using this bound, it is shown that the for the universe as an expanding thermodynamical system, the total effective Komar energy never exceeds the square of the expansion rate with a factor of $\frac{3}{4π}$.

gr-qc↗

arXiv2017

Braneworld Black Holes and Entropy Bounds

The Bousso's D-bound entropy for the various possible black hole solutions on a 4-dimensional brane is checked. It is found that the D-bound entropy here is apparently different from that of obtained for the 4-dimensional black hole solutions. This difference is interpreted as the extra loss of information, associated to the extra dimension, when an extra-dimensional black hole is moved outward the observer's cosmological horizon. Also, it is discussed that N-bound entropy is hold for the possible solutions here. Finally, by adopting the recent Bohr-like approach to black hole quantum physics for the excited black holes, the obtained results are written also in terms of the black hole excited states.

gr-qc↗

arXiv2016

Emergent Universe in the Braneworld Scenario

According to Padmanabhan's proposal, the difference between the surface degrees of freedom and the bulk degrees of freedom in a region of space may result in the acceleration of Universe expansion through the relation $ΔV/Δt = N_{\rm sur}-N_{\rm bulk}$ where $N_{\rm bulk}$ and $N_{\rm sur}$ are referred to the degrees of freedom related to the matter and energy content inside the bulk and surface area, respectively \cite{Pad1}. In this paper, we study the dynamical effect of the extrinsic geometrical embedding of an arbitrary four dimensional brane in a higher dimensional bulk space and investigate the corresponding degrees of freedom. Considering the modification of Friedmann equations arising from a general braneworld scenario, we obtain a correction term in Padmanabhan's relation, denoting the number of degrees of freedom related to the extrinsic geometry of the brane embedded in higher dimensional spacetime as $ΔV /Δt=N_{\rm sur}-N_{\rm bulk}-N_{\rm extr}$ where $N_{\rm extr}$ is referred to the degree of freedom related to the extrinsic geometry of the brane while $N_{\rm sur}$ and $N_{\rm bulk}$ are as well as before. Finally, we study the validity of the first and second laws of thermodynamics for this general braneworld scenario in the state of thermal equilibrium and in the presence of confined matter fields to the brane with the induced geometric matter fields.

gr-qc↗