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Probing the cosmology of f(Q,T) gravity with holographic background fluid Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-03-15 Khandro K. Chokyi, Surajit Chattopadhyay
In this work, we have investigated the cosmology of holographic origin within modified f(Q,T) gravity framework by employing different forms of the scale factor viz. power law, intermediate, emergent, and logamediate forms. The reconstruction of f(Q,T) gravity is done by assuming the generalized Holographic Dark Energy as the background fluid where the IR cut-off is considered (αH2+βḢ). We consider
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Null geodesic structure for the Barriola–Vilenkin spacetime via k-essence Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-03-15 Bivash Majumder, Saibal Ray, Goutam Manna
Based on the work of Chandrasekhar [The Mathematical Theory of Black Holes, Chap. 3, Sec. 20 (Oxford University Press, 1992)], we investigate the null geodesic structure of the emergent Barriola–Vilenkin (BV) spacetime in the context of k-essence theory. For k-essence, the emergent gravity metric is a one-to-one correspondence with the BV metric connected to the Schwarzschild background, where the
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Induced polar perturbations with stochastic effects in dense matter relativistic stars: A theoretical probe at intermediate sub-hydro mesoscopic scales Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-03-15 Seema Satin
A linear response relation between metric and fluid perturbations driven by a background internal noise source is used as a framework for addressing stochastic effects in order to establish a mesoscopic theory for dense matter relativistic stars. In this paper, nonradial polar perturbations are worked out, which are important from the point of view of detection in future. We present qualitative first
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Magnetic fields in inhomogeneous axion stars Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-24 Petr Akhmetiev, Maxim Dvornikov
We study the time evolution of magnetic fields in various configurations of spatially inhomogeneous pseudoscalar fields, which are the coherent superposition of axions. The new induction equation for the magnetic field, which accounts for this inhomogeneity, is derived for such systems. Based on this equation, we study, first, the evolution of two Chern–Simons (CS) waves interacting with a linearly
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Effective potential in non-perturbative gauge theories Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-21 Gianluca Calcagni, Marco Frasca, Anish Ghoshal
We consider a formalism to describe the false-vacuum decay of a scalar field in gauge theories in non-perturbative regimes. We find that the larger the gauge coupling with respect to the self-coupling of the scalar, the shallower the local minimum of the unstable vacuum, to the point where it disappears. This offers the possibility to obtain a consistent picture of early universe cosmology: at high
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Gravitational instability of nonuniformly rotating and magnetized viscoelastic fluid with dissipative effects Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-21 Joginder Singh Dhiman, Mehak Mahajan
In this paper, the effect of dissipative energy arising from bulk-viscosity on the collapse of a self-gravitating viscoelastic medium permeated with a nonuniform magnetic field and rotation is analyzed using the standard Jeans mechanism. A local solution of the system of nondimensional linearized perturbation equations, having variable coefficients, is obtained using the normal modes analysis method
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Cosmological dynamics and observational constraints on a viable f(Q) nonmetric gravity model Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-19 A. Oliveros, Mario A. Acero
Inspired by an exponential f(R) gravity model studied in the literature, in this work we introduce a new and viable f(Q) gravity model, which can be represented as a perturbation of ΛCDM. Typically, within the realm of f(Q) gravity, the customary approach to investigate cosmological evolution involves employing a parametrization of the Hubble expansion rate in terms of the redshift, H(z), among other
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The thirty meter telescope at mount Mauna Kea: A long history of its developments Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-14 Rishab Singha, Soham Ray, Nirbhay Mishra, Saibal Ray
In this paper, we present the historical background of the Thirty-Meter Telescope at Mount Mauna Kea and a few facts regarding scientific advancement. However, we will not focus on any politically motivated matters and ethical issues, rather our sincere concern is to highlight the overall history, philosophy, science and technology which have prevailed for any civilized advancement of the society.
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Diffeomorphism invariance and quantum mechanical paradoxes Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-07 Adam Dukehart, David Mattingly
Paradoxes in gravitational physics, such as grandfather paradoxes with closed timelike curves or the AMPS paradox, are often constructed in a weak gravity regime but upon further examination engender strong gravitational responses such as unstable Cauchy horizons or firewalls. In contrast, some proposed paradoxes in nonrelativistic quantum mechanics ignore gravity completely. Such nonrelativistic proposed
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Unimodular-like times, evolution and Brans–Dicke gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-07 Paolo M. Bassani, João Magueijo
In unimodular-like theories, the constants of nature are demoted from pre-given parameters to phase space variables. Their canonical duals provide physical time variables. We investigate how this interacts with an alternative approach to varying constants, where they are replaced by dynamical scalar fields. Specifically, we investigate the Brans–Dicke theory of gravity and its interaction with clocks
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Primordial cosmology of an emergent-like universe from modified gravity: Reconstruction and phenomenology optimization with a genetic algorithm Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-05 V. K. Oikonomou, Gregory Kafanelis
General relativity has been the dominant paradigm theory of gravity for the last century, it manages to explain a plethora of astronomical and cosmological observations with high accuracy. A major challenge faced by general relativity is, that it predicts a singularity as the beginning of our universe. In this paper, we shall explore a well-known idea in the literature that of the emergent universe
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Gravitational wave: Generation and detection techniques Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-02-05 Saibal Ray, R. Bhattacharya, Sanjay K. Sahay, Abdul Aziz, Amit Das
In this paper, we review the theoretical basis for generation of gravitational waves and the detection techniques used to detect a gravitational wave. To materialize this goal in a thorough way, we first start with a mathematical background for general relativity from which a clue for gravitational wave was conceived by Einstein. Thereafter, we give the classification scheme of gravitational waves
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Equilibrium of charged fluid around a Kerr black hole immersed in a magnetic field: Variation of angular momentum Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-01-31 Audrey Trova
This work presents analytically constructed equilibrium structures of charged perfect fluids orbiting Kerr Black holes embedded in an asymptotically uniform magnetic field. Our focus is on the effect of the nonconstant angular momentum distribution through the disk, as well as its combined effect with the external magnetic field and the fluid charge. We demonstrate that the three parameters of our
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Unveiling the fifth state of matter: Insights into ultra-hot plasma and its applications Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2024-01-29 Mohammad Mehdi Bagheri-Mohagheghi, Behnam Pourhassan, Emmanuel Saridakis, Salvatore Capozziello, Prabir Rudra
This paper presents a study of the dissociation energy of the N–S poles of a quantum magnetic particle, carried out from both classical and quantum mechanical perspectives. A simple model of a harmonic oscillator is employed to estimate the dissociation energy of the N–S poles, as well as the corresponding breakdown temperature and internal pressure. The results indicate that the separation of magnetic
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Balancing multiple charge particle excesses with baryon asymmetry Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-11-15 Vitaly A. Beylin, Maxim Yu. Khlopov, Danila O. Sopin
Stable multiple charged particles can possess electroweak charges, as per the walking technicolor models. An asymmetry of these particles is balanced by sphaleron transitions which among other things can provide an excess of baryons and/or leptons. A possibility to generate sufficient amount of particles with the charge −2n to explain the observed dark matter density by dark atoms (which are bound
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Shadows near supermassive black holes: From a theoretical concept to GR test Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-09-06 Alexander F. Zakharov
General relativity (GR) passed many astronomical tests but in majority of them GR predictions have been tested in a weak gravitational field approximation. Around 50 years ago a shadow was introduced by Bardeen as a purely theoretical concept but due to an enormous progress in observational and computational facilities this theoretical prediction has been confirmed and the most solid argument for an
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Characterizations of weakly Ricci-symmetric spacetimes and f(ℛ)-gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-22 Uday Chand De, Dipankar Hazra
In this paper, we characterize weakly Ricci-symmetric (shortly, (WRS)4) spacetimes and their solutions in f(ℛ)-gravity. It is demonstrated that a (WRS)4 spacetime represents a stiff matter fluid. In addition, we obtain that a conformally flat (WRS)4 spacetime is a space of quasi-constant sectional curvature. Moreover, we establish that a Ricci symmetric (WRS)4 spacetime represents a static spacetime
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Universality in binary black hole dynamics: An integrability conjecture Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-21 José Luis Jaramillo, Badri Krishnan, Carlos F. Sopuerta
The waveform of a binary black hole coalescence appears to be both simple and universal. In this essay we argue that the dynamics should admit a separation into “fast and slow” degrees of freedom, such that the latter are described by an integrable system of equations, accounting for the simplicity and universality of the waveform. Given that Painlevé transcendents are a smoking gun of integrable structures
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In search of the maximum lost momentum Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-21 Carlos O. Lousto, James Healy
We performed a series of 1381 full numerical simulations of high energy collision of two black holes to search for the maximum recoil velocity after their merger. We studied equal mass binaries with opposite spins pointing along the orbital plane to maximize asymmetric gravitational radiation and performed a search of spin orientations in the plane, impact parameters, and initial linear momenta to
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Pancakification and negative Hawking temperatures Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-21 Tyler McMaken
Vacuum models of charged or spinning black holes possess two horizons, the inner of which has the oft-overlooked property that gravitational tidal forces initially spaghettifying a freely falling observer will eventually change signs and flatten the observer like a pancake. Inner horizons also may induce a classical blueshift instability known as mass inflation, and a number of recent studies have
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Stability analysis of f(Q) gravity models using dynamical systems Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-21 Pooja Vishwakarma, Parth Shah
In recent years, the modified theory of gravity known as f(Q) gravity has drawn interest as a potential alternative to general relativity. According to this theory, the gravitational force is determined by a function of the so-called “non-metricity” tensor Q, which expresses how far a particle space-time is from the metric geometry. In contrast to general relativity, which describes the gravitational
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Reconstructing the parameter space of nonanalytical cosmological fixed points Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-21 Santiago García-Serna, J. Bayron Orjuela-Quintana, César A. Valenzuela-Toledo, Hernán Ocampo Durán
Dynamical system theory is a widely used technique in the analysis of cosmological models. Within this framework, the equations describing the dynamics of a model are recast in terms of dimensionless variables, which evolve according to a set of autonomous first-order differential equations. The fixed points of this autonomous set encode the asymptotic evolution of the model. Usually, these points
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Nonlinear sigma models in inflationary cosmology Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-10 Abhishek Goswami
Nonlinear Sigma Models in two dimensions (NLSM2) describe the quantum-field theory (QFT) of the Embedding map from a two-dimensional surface to a higher dimensional target space. We assume that before the big bang the universe was an abstract space with a two-dimensional surface embedded in it. We study QFT of the Embedding map in the universe that is NLSM2. We consider the abstract target space which
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Fermion localization mechanisms in f(T,𝒯 )-brane Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-09 A. R. P. Moreira
In this work, we investigate two mechanisms for locating fermions on the brane in a modified teleparallel gravity f(T,𝒯), where T is the torsion scalar and 𝒯 is the trace of the energy–momentum tensor. The first mechanism is a Yukawa-type minimal coupling between the fermion and the background scalar field. The second mechanism is a nonminimal coupling between the fermion and the torsion. The geometric
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Black hole entropy contributions from Euclidean cores Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-02 Jens Boos
The entropy of a Schwarzschild black hole, as computed via the semiclassical Euclidean path integral in a stationary phase approximation, is determined not by the on-shell value of the action (which vanishes), but by the Gibbons–Hawking–York boundary term evaluated on a suitable hypersurface, which can be chosen arbitrarily far away from the horizon. For this reason, the black hole singularity seemingly
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Punctuated chaos and indeterminism in self-gravitating many-body systems Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-08-01 Tjarda C. N. Boekholt, Simon F. Portegies Zwart, Douglas C. Heggie
Dynamical chaos is a fundamental manifestation of gravity in astrophysical, many-body systems. The spectrum of Lyapunov exponents quantifies the associated exponential response to small perturbations. Analytical derivations of these exponents are critical for understanding the stability and predictability of observed systems. This paper presents a new model for chaos in systems with eccentric and crossing
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On Chaplygin models in f(G) gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-29 Fidele Twagirayezu, Abraham Ayirwanda, Albert Munyeshyaka, Solange Mukeshimana, Joseph Ntahompagaze, Leon Fidele Ruganzu Uwimbabazi
This work treats cosmological perturbation in a mixture of standard matter, Chaplygin gas as well as Gauss–Bonnet fluids using a 1+3 covariant approach in the context of modified f(G) gravity. We define the gradient variables to obtain linear perturbation equations. After scalar and redshift transformations, we consider both an original Chaplygin and generalized Chaplygin gas models under Gauss–Bonnet
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BMS symmetry in gravity: Front form versus Instant form Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-28 Sudarshan Ananth, Sucheta Majumdar
In general relativity, the allowed set of diffeomorphisms or gauge transformations at asymptotic infinity forms the BMS group, an infinite-dimensional extension of the Poincaré group. We focus on the structure of the BMS group in two distinct forms of Hamiltonian dynamics — the instant and front forms. Both similarities and differences in these two forms are examined while emphasizing the role of noncovariant
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The virial theorem for retarded gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-28 Asher Yahalom
Galaxy Clusters are huge physical systems having a generic size of tens of millions of light years. Thus any modification at the center of the cluster will affect the outskirts only tens of millions of years afterwards. Those retardation considerations seem to be neglected in present day analysis used to estimate the total mass of the galaxy cluster, including those estimates which are based on the
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The sound of the event horizon Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-28 R. A. Konoplya
During the ringdown phase of a gravitational signal emitted by a black hole, the least damped quasinormal frequency dominates. If modifications to Einstein’s theory induce noticeable deformations of the black-hole geometry only near the event horizon, the fundamental mode remains largely unaffected. However, even a small change near the event horizon can significantly impact the first few overtones
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Matter–gravity entanglement entropy and the second law for black holes Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-27 Bernard S. Kay
Hawking showed that a black hole formed by collapse will emit radiation and eventually disappear. We address the challenge to define an objective notion of physical entropy which increases throughout this process in a way consistent with unitarity. We have suggested that (instead of coarse-grained entropy) physical entropy is matter–gravity entanglement entropy and that this may offer an explanation
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Dynamic dark energy from the local limit of nonlocal gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-27 Javad Tabatabaei, Abdolali Banihashemi, Shant Baghram, Bahram Mashhoon
Nonlocal gravity (NLG), a classical extension of Einstein’s theory of gravitation, has been studied mainly in linearized form. In particular, nonlinearities have thus far prevented the treatment of cosmological models in NLG. In this essay, we discuss the local limit of NLG and apply this limit to the expanding homogenous and isotropic universe. The theory only allows spatially flat cosmological models;
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Buchdahl-inspired spacetimes and wormholes: Unearthing Hans Buchdahl’s other “hidden” treasure trove Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-25 Hoang Ky Nguyen
Circa 1962 Hans A. Buchdahl pioneered a program — and made significant progress — seeking vacuo configurations in pure ℛ2 gravity (H. A. Buchdahl, Nuovo Cimento23 (1962) 141). Unfortunately, he deemed the final step in his calculations impassable and prematurely suspended his pursuit. Since then, his achievements on this front have faded into dormancy. Unbeknownst to Buchdahl himself, the ℛ2 vacua
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Fast radio bursts signal high-frequency gravitational waves Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-25 Ashu Kushwaha, Sunil Malik, S. Shankaranarayanan
There is growing evidence for high-frequency gravitational waves (HFGWs) ranging from MHz to GHz. Several HFGW detectors have been operating for over a decade, and two GHz events have been reported recently. However, a confirmed detection might take a decade. This essay argues that unexplained observed astrophysical phenomena, like Fast Radio Bursts (FRBs), might provide indirect evidence for HFGWs
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Nomen non est omen: Why it is too soon to identify ultra-compact objects as black holes Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-25 Sebastian Murk
Black holes play a pivotal role in the foundations of physics, but there is an alarming discrepancy between what is considered to be a black hole in observational astronomy and theoretical studies. Despite claims to the contrary, we argue that identifying the observed astrophysical black hole candidates as genuine black holes is not justified based on the currently available observational data, and
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Stellar equilibrium on a physical vacuum soil Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-22 Julio Arrechea, Carlos Barceló
We show that the repulsive effects associated to the zero-point energies of quantum fields are capable of supporting ultracompact stars that overcome the compactness limits present in general relativity for any object in hydrostatic equilibrium. These objects are exact self-consistent solutions in semiclassical gravity that incorporate the backreaction of the renormalized stress-energy tensor (RSET)
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Constraining the bounce realization with holographic background and analytical exploration of the consequences in a modified gravity framework Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-21 Moli Ghosh, Surajit Chattopadhyay
The work reported in this paper explores holographic bounce. In the first phase of the study, we chose a non-singular bouncing scale factor. Then we reconstructed f(T) gravity and analytically derived constraints on the bouncing parameter σ. These constraints helped us understand the scale factor’s quintessence or phantom behavior. Furthermore, we also explored the statefinder parameters for reconstructed
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A new class of generalized Ellis–Bronnikov wormhole in asymptotically safe gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-21 Nisha Godani, Shubham Kala
In this paper, the asymptotically safe gravity has been taken in the gravitational action to derive the wormhole solutions. The paper is aimed at the study of traversable wormhole solutions having repulsive geometry at the throat. The wormhole solutions are produced in two cases: the first case includes the logarithmic form of the shape function while in the second case, the shape function is derived
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Cosmological application of the Maxwell gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-21 Salih Kibaroğlu
In this study, we consider a cosmological model for the Maxwell gravity which is constructed by gauging the semi-simple extended Poincaré algebra. Inspired by the Einstein–Yang–Mills theory, we describe the Maxwell gauge field in terms of two additional time-dependent scalar fields. Within the context of a homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker universe, we derive the Friedmann
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What are neutron stars made of? Gravitational waves may reveal the answer Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-21 Neil Lu, Susan M. Scott, Karl Wette
Neutron stars are one of the most mysterious wonders in the universe. Their extreme densities hint at new and exotic physics at work within. Gravitational waves could be the key to unlocking their secrets. In particular, a first detection of gravitational waves from rapidly-spinning, deformed neutron stars could yield new insights into the physics of matter at extreme densities and under strong gravity
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Event horizon detection: Zenith view as seen by falling into a Schwarzschild black hole Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-20 Yukiyoshi Iida
To visualize what is seen by an observer in curved spacetime, both general relativistic effects and special relativistic effects need to be considered. In this study, the author analytically proved that the zenith view seen by an observer falling freely into a Schwarzschild black hole (that is, the observer’s view of the point on the opposite side of the black hole) becomes enlarged, “redder,” and
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The universality of black hole thermodynamics Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-20 Samir D. Mathur, Madhur Mehta
The thermodynamic properties of black holes — temperature, entropy and radiation rates — are usually associated with the presence of a horizon. We argue that any extremely compact object (ECO) must have the same thermodynamic properties. Quantum fields just outside the surface of an ECO have a large negative Casimir energy similar to the Boulware vacuum of black holes. If the thermal radiation emanating
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On the inevitable lightness of vacuum Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-20 Laurent Freidel, Jerzy Kowalski-Glikman, Robert G. Leigh, Djordje Minic
In this essay, we present a new understanding of the cosmological constant problem, built upon the realization that the vacuum energy density can be expressed in terms of a phase space volume. We introduce a UV-IR regularization which implies a relationship between the vacuum energy and entropy. Combining this insight with the holographic bound on entropy then yields a bound on the cosmological constant
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Emergence of quantum-field theory in causal diamonds Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-17 Tom Banks
The experimental successes of quantum-field theory do not justify using it to describe even a finite fraction of the entanglement entropy of a causal diamond with its exterior, in the limit of large diamonds. Susskind and Uglum and Jacobson conjectured that this divergent entropy could be thought of as a renormalization of Newton’s constant in the Bekenstein–Hawking formula, if we applied that formula
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Born reciprocity and discretized Finsler structure: An approach to quantize GR curvature tensors on three-sphere Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-12 Abdel Nasser Tawfik, Tahia F. Dabash
At relativistic energies and finite magnetic fields, the noncommutative relation of distance and momentum, the Heisenberg uncertainty principle, the fundamental theory of quantum mechanics, is conjectured to get modifications. Results from various rigorous approaches to quantum gravity, such as string theory, loop quantum gravity and doubly special relativity support the generalization of the noncommutative
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Thermal radiation of thin accretion disk around Taub-NUT black hole Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-07-10 Bakhtiyor Narzilloev, Bobomurat Ahmedov
The effects of a gravitomagnetic charge on the thermal radiation properties of a thin accretion disk surrounding a non-rotating black hole are studied. The studied system consists of a non-rotating black hole with a non-zero gravitomagnetic charge and a Novikov–Thorne disk that is thin and optically thick. It is found that the gravitomagnetic charge enhances the gravitational field of the central black
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Black holes that are too cold to respect cosmic censorship Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-30 Shahar Hod
In this essay, it is proved that there are black holes that are dangerously cold. In particular, by analyzing the emission spectra of highly charged black holes we reveal the fact that near-extremal black holes whose Bekenstein–Hawking temperatures lie in the regime TBH≲me6/e3 may turn into horizonless naked singularities, thus violating the cosmic censorship principle, if they emit a photon with the
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Quantum black holes as classical space factories Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-30 A. Iorio, L. Smaldone
Space and matter may both be manifestations of a single fundamental quantum dynamics, as it may become evident during black-hole evaporation. Inspired by the fact that quantum electrodynamics underlies the classical theory of elasticity, that in turn has a natural and well-known geometric description in terms of curvature and torsion, related to topological defects, here we move some necessary steps
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Equivalence principle, de-Sitter space, and cosmological twistors Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-28 Maciej Dunajski
In this paper, I discuss the impact of the positive cosmological constant on the interplay between the equivalence principle in general relativity, and the rules of quantum mechanics. At the nonrelativistic level, there is an ambiguity in the definition of a phase of a wave function measured by inertial and accelerating observes. This is the cosmological analogue of the Penrose effect, which can also
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Energy conditions of traversable wormhole in the deformed f(R) gravitational model Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-28 J. Sadeghi, S. Noori Gashti, M. R. Alipour, M. A. S. Afshar
One of the most important issues in cosmology is the study of a series of hypothetical objects called wormholes. Recently, researchers have studied these hypothetical objects under different conditions. In this paper, we aim to evaluate the traversable wormhole according to a modified f(R) gravitational model, specifically −R2+aR2(1−n), from the perspective of two essential functions in wormhole structure:
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Dynamical system approach of interacting dark energy models with minimally coupled scalar field Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-23 Amit Samaddar, S. Surendra Singh, Md Khurshid Alam
We investigated the stability condition of f(Q) gravity theory with interacting and noninteracting models by using dynamical system. We assume the f(Q) function as f(Q)=Q+M22, where M is the free parameter. We evaluated the critical points for this model and examined the stability behavior. We found two stable critical points for interacting model. The phase plots for this system are examined and the
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Conformal motions of anisotropic exact Bianchi type II models admitting energy conditions in f(T) gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-21 Sabiha Qazi, Fiaz Hussain, M. Ramzan, Sirajul Haq
The purpose of this paper is to explore the anisotropic exact Bianchi type II solutions in f(T) gravity, where T denotes the torsion scalar. We utilize the solutions to discuss conformal vector fields (CVFs) and energy conditions. In the first slot of this study, we find the CVFs. The CVFs being a generalization of the Killing vector fields (KVFs) are affiliated with the conservation laws of physics
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Dark matter in a bi-metric universe Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-19 Carlos Maldonado, Fernando Méndez
We study the possibility to describe dark matter in a model of the universe with two-scale factors and a nonstandard Poisson bracket structure characterized by the deformation parameter κ. The dark matter evolution is analyzed in the early stages of the universe, and its relic density is obtained via the Freeze-In and Freeze-Out mechanism. We show that by fixing κ and the initial ratio of energy densities
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The semiclassical limit of quantum gravity and the problem of time Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-17 R. I. Ayala Oña, M. B. Kalmykov, D. P. Kislyakova, T. P. Shestakova
The question about the appearance of time in the semiclassical limit of quantum gravity continues to be discussed in the literature. It is believed that a temporal Schrödinger equation for matter fields on the background of a classical gravitational field must be true. To obtain this equation, the Born–Oppenheimer approximation for gravity is used. However, the origin of time in this equation is different
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Born reciprocity and relativistic generalized uncertainty principle in Finsler structure: Fundamental tensor in discretized curved spacetime Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-17 Abdel Nasser Tawfik, Tahia F. Dabash
The main findings of the generalized uncertainty principle (GUP), the phenomenological approach, for instance, the emergence of a minimal measurable length uncertainty, are obtained in various versions from theories of quantum gravity, such as string theory, loop quantum gravity, doubly special relativity and black hole physics. GUP counts for impacts of relativistic energies and finite gravitational
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On de Sitter spacetime and string theory Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-15 Per Berglund, Tristan Hübsch, Djordje Minic
We review various aspects of de Sitter spacetime in string theory: its status as an Effective Field Theory spacetime solution, its relation to the vacuum energy problem in string theory, its (global) holographic definition in terms of two entangled and noncanonical conformal field theories as well as a realization of a realistic de Sitter universe endowed with the observed visible matter and the necessary
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On 1 + 3 covariant perturbations of the quasi-Newtonian spacetime in modified Gauss–Bonnet gravity Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-15 Albert Munyeshyaka, Joseph Ntahompagaze, Tom Mutabazi, Manasse R. Mbonye
The consideration of a 1+3 covariant approach to cold dark matter universe with no shear cosmological dust model with irrotational flows is developed in the context of f(G) gravity theory in this study. This approach reveals the existence of integrability conditions which do not appear in noncovariant treatments. We constructed the integrability conditions in modified Gauss–Bonnet f(G) gravity basing
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On quantum traversability of wormholes Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-15 J. Furtado, C. R. Muniz, M. S. Cunha, J. E. G. Silva
This paper explores the possibility of scalar quantum particles traversing generalized Ellis–Bronnikov wormholes, taking into account quantum effects like tunneling. We investigate the generalized Ellis–Bronnikov wormhole metric and discover that when the exponent parameter is n=2, there is a single barrier-shaped effective potential at the throat of the wormhole for any orbital angular momentum value
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Dynamical analysis of the Tsallis holographic dark energy models with event horizon as cut-off and interaction with matter Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-12 A. V. Astashenok, A. S. Tepliakov
The model of generalized Tsallis holographic dark energy (which is known to be particular representative of Nojiri–Odintsov HDE) with event horizon as cut-off is investigated using methods of dynamical analysis. We take into consideration possible interaction with dark energy and matter in various forms. Critical points are determined. Cosmological evolution of the universe depends from interaction
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A MacDowell–Mansouri-type formulation for conformally flat Einstein manifolds Int. J. Mod. Phys. D (IF 2.2) Pub Date : 2023-06-12 J. E. Rosales-Quintero
We study a pure connection formulation plus algebraic constraints in four spacetime dimensions where the gauge group G⊃SO(1,3). We show that the action has, as particular cases, the MacDowell–Mansouri and the Stelle–West formulations for gravity. Also, under adequate specification of the constraint terms, we obtain a subset of Einstein manifolds that are torsionless conformally flat manifolds.