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  • Semi-Classical Einstein Equations: Descend to the Ground State
    Universe (IF 2.165) Pub Date : 2020-05-29
    Zbigniew Haba

    The time-dependent cosmological term arises from the energy-momentum tensor calculated in a state different from the ground state. We discuss the expectation value of the energy-momentum tensor on the right hand side of Einstein equations in various (approximate) quantum pure as well as mixed states. We apply the classical slow-roll field evolution as well as the Starobinsky and warm inflation stochastic

  • Numerical Investigation for Periodic Orbits in the Hill Three-Body Problem
    Universe (IF 2.165) Pub Date : 2020-05-28
    Vassilis S. Kalantonis

    The current work performs a numerical study on periodic motions of the Hill three-body problem. In particular, by computing the stability of its basic planar families we determine vertical self-resonant (VSR) periodic orbits at which families of three-dimensional periodic orbits bifurcate. It is found that each VSR orbit generates two such families where the multiplicity and symmetry of their member

  • Obscuration and Scattering in Narrow-Line Seyfert 1s
    Universe (IF 2.165) Pub Date : 2020-05-28
    Xiang Pan; Hongyan Zhou; Peng Jiang

    Narrow-line Seyfert 1s (NLS1s) observed at large inclinations from face-on are important for understanding this amazing AGN subclass. However, progress is slowly being made in the huntings and studies of highly obscured ( ≥ 1 ) NLS1s . Recently, we discovered that multi-wavelength photometric and polarimetric analysis can be of great help in identifying and studying highly obscured NLS1s. This paper

  • Cosmic Analogues of Classic Variational Problems
    Universe (IF 2.165) Pub Date : 2020-05-27
    Valerio Faraoni

    Several classic one-dimensional problems of variational calculus originating in non-relativistic particle mechanics have solutions that are analogues of spatially homogeneous and isotropic universes. They are ruled by an equation which is formally a Friedmann equation for a suitable cosmic fluid. These problems are revisited and their cosmic analogues are pointed out. Some correspond to the main solutions

  • Significance of Black Hole Visualization and Its Implication for Science Education Focusing on the Event Horizon Telescope Project
    Universe (IF 2.165) Pub Date : 2020-05-25
    Hye-Gyoung Yoon; Jeongwoo Park; Insun Lee

    In recent years, substantial progress has been made in black hole visualization. However, there is a lack of essential up-to-date information regarding black holes in current school curricula, in spite of students’ substantial interest in black holes. In this study, we examined the implications of the Event Horizon Telescope project, a recent achievement of the scientific community, for science education

  • Localization of Energy and Momentum in an Asymptotically Reissner-Nordström Non-Singular Black Hole Space-Time Geometry
    Universe (IF 2.165) Pub Date : 2020-05-23
    Irina Radinschi; Pradyumn Kumar Sahoo; Theophanes Grammenos; Surajit Chattopadhyay; Marius-Mihai Cazacu

    The space-time geometry exterior to a new four-dimensional, spherically symmetric and charged black hole solution that, through a coupling of general relativity with a non-linear electrodynamics, is non-singular everywhere, for small r it behaves as a de Sitter metric, and asymptotically it behaves as the Reissner-Nordström metric, is considered in order to study energy-momentum localization. For the

  • The Jet-Disk Coupling of Seyfert Galaxies from a Complete Hard X-ray Sample
    Universe (IF 2.165) Pub Date : 2020-05-10
    Xiang Liu; Ning Chang; Zhenhua Han; Xin Wang

    We analyze the jet-disk coupling for different subsamples from a complete hard X-ray Seyfert sample to study the coupling indices and their relation to accretion rate. The results are: (1) the power-law coupling index ranges from nearly unity (linear correlation) for radio loud Seyferts to significantly less than unity for radio quiet ones. This decline trend of coupling index also holds from larger

  • Evidence of Time Evolution in Quantum Gravity
    Universe (IF 2.165) Pub Date : 2020-05-08
    Sergey Cherkas and Vladimir Kalashnikov

    In this paper, we argue that the problem of time is not a crucial issue inherent in the quantum picture of the universe evolution. On the minisuperspace model example with the massless scalar field, we demonstrate four approaches to the description of quantum evolution, which give similar results explicitly. The relevance of these approaches to building a quantum theory of gravity is discussed.

  • Mass in de Sitter and Anti-de Sitter Universes with Regard to Dark Matter
    Universe (IF 2.165) Pub Date : 2020-05-05
    Jean-Pierre Gazeau

    An explanation of the origin of dark matter is suggested in this work. The argument is based on symmetry considerations about the concept of mass. In Wigner’s view, the rest mass and the spin of a free elementary particle in flat space-time are the two invariants that characterize the associated unitary irreducible representation of the Poincaré group. The Poincaré group has two and only two deformations

  • Cosmological Finsler Spacetimes
    Universe (IF 2.165) Pub Date : 2020-05-05
    Manuel Hohmann; Christian Pfeifer; Nicoleta Voicu

    Applying the cosmological principle to Finsler spacetimes, we identify the Lie Algebra of symmetry generators of spatially homogeneous and isotropic Finsler geometries, thus generalising Friedmann-Lemaître-Robertson-Walker geometry. In particular, we find the most general spatially homogeneous and isotropic Berwald spacetimes, which are Finsler spacetimes that can be regarded as closest to pseudo-Riemannian

  • On the Non Metrizability of Berwald Finsler Spacetimes
    Universe (IF 2.165) Pub Date : 2020-05-01
    Andrea Fuster; Sjors Heefer; Christian Pfeifer; Nicoleta Voicu

    We investigate whether Szabo’s metrizability theorem can be extended to Finsler spaces of indefinite signature. For smooth, positive definite Finsler metrics, this important theorem states that, if the metric is of Berwald type (i.e., its Chern–Rund connection defines an affine connection on the underlying manifold), then it is affinely equivalent to a Riemann space, meaning that its affine connection

  • Estimation of Electrical Conductivity and Magnetization Parameter of Neutron Star Crusts and Applied to the High-Braking-Index Pulsar PSR J1640-4631
    Universe (IF 2.165) Pub Date : 2020-05-01
    Hui Wang; Zhi-Fu Gao; Huan-Yu Jia; Na Wang; Xiang-Dong Li

    Young pulsars are thought to be highly magnetized neutron stars (NSs). The crustal magnetic field of a NS usually decays at different timescales in the forms of Hall drift and Ohmic dissipation. The magnetization parameter ω B τ is defined as the ratio of the Ohmic timescale τ O h m to the Hall drift timescale τ H a l l . During the first several million years, the inner temperature of the newly born

  • Roto-Chemical Heating with Fall-Back Disk Accretion in the Neutron Stars Containing Quark Matter
    Universe (IF 2.165) Pub Date : 2020-04-30
    Wei Wei; Xin-Yu Xu; Kai-Tuo Wang; Xiao-Hang Ma

    Probing quark matter is one of the important tasks in the studies of neutron stars (NS). Some works explicitly consider the existence of quark matter in the appearance of hybrid star (HS) or pure quark star (QS). In the present work, we study the roto-chemical heating with accretion in HS and QS, and compare their chemical evolution and cooling features with pure NS. Different from HS and NS, there

  • Aspects of Relativistic Heavy-Ion Collisions
    Universe (IF 2.165) Pub Date : 2020-04-30
    Georg Wolschin

    The rapid thermalization of quarks and gluons in the initial stages of relativistic heavy-ion collisions is treated using analytic solutions of a nonlinear diffusion equation with schematic initial conditions, and for gluons with boundary conditions at the singularity. On a similarly short time scale of t ≤ 1 fm/c, the stopping of baryons is accounted for through a QCD-inspired approach based on the

  • Automated Classification of Massive Spectra Based on Enhanced Multi-Scale Coded Convolutional Neural Network
    Universe (IF 2.165) Pub Date : 2020-04-23
    Bin Jiang; Donglai Wei; Jiazhen Liu; Shuting Wang; Liyun Cheng; Zihao Wang; Meixia Qu

    The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has produced massive medium-resolution spectra. Data mining for special and rare stars in massive LAMOST spectra is of great significance. Feature extraction plays an important role in the process of automatic spectra classification. The proper classification network can extract most of the common spectral features with minimum

  • On the Analyticity of Static Solutions of a Field Equation in Finsler Gravity
    Universe (IF 2.165) Pub Date : 2020-04-22
    Erasmo Caponio; Antonio Masiello

    It is well-known that static vacuum solutions of Einstein equations are analytic in suitable coordinates. We ask here for an extension of this result in the context of Finsler gravity. We consider Finsler spacetimes that retain several properties of static Lorentzian spacetimes, are Berwaldand have vanishing Ricci scalar.

  • Editorial to the Special Issue “Probing New Physics with Black Holes”
    Universe (IF 2.165) Pub Date : 2020-04-22
    Aurélien Barrau

    Black holes are fantastic laboratories for probing new physics. Both theoretically and experimentally, many new ideas are emerging to use them as tools for understanding better quantum gravity or classical gravity beyond general relativity. I briefly review some new results.

  • Numerical Modelling of Satellite Downlink Signals in a Finslerian-Perturbed Schwarzschild Spacetime
    Universe (IF 2.165) Pub Date : 2020-04-20
    Ingo Abraham; Wolfgang Hasse; Martin Plato

    The work presented in this paper aims to contribute to the problem of testing Finsler gravity theories by means of experiments and observations in the solar system. Within a class of spherically symmetric static Finsler spacetimes we consider a satellite with an on-board atomic clock, orbiting in the Finslerian-perturbed gravitational field of the earth, whose time signal is transmitted to a ground

  • Generalised Uncertainty Relations for Angular Momentum and Spin in Quantum Geometry
    Universe (IF 2.165) Pub Date : 2020-04-19
    Matthew J. Lake; Marek Miller; Shi-Dong Liang

    We derive generalised uncertainty relations (GURs) for orbital angular momentum and spin in the recently proposed smeared-space model of quantum geometry. The model implements a minimum length and a minimum linear momentum and recovers both the generalised uncertainty principle (GUP) and extended uncertainty principle (EUP), previously proposed in the quantum gravity literature, within a single formalism

  • Foundations of Finsler Spacetimes from the Observers’ Viewpoint
    Universe (IF 2.165) Pub Date : 2020-04-16
    Antonio N. Bernal; Miguel A. Javaloyes; Miguel Sánchez

    Physical foundations for relativistic spacetimes are revisited in order to check at what extent Finsler spacetimes lie in their framework. Arguments based on inertial observers (as in the foundations of special relativity and classical mechanics) are shown to correspond with a double linear approximation in the measurement of space and time. While general relativity appears by dropping the first linearization

  • High-Energy and Very High-Energy Constraints from Log-Parabolic Spectral Models in Narrow-Line Seyfert 1 Galaxies
    Universe (IF 2.165) Pub Date : 2020-04-16
    Stefano Vercellone; Luigi Foschini; Patrizia Romano; Markus Böttcher; Catherine Boisson

    Narrow-line Seyfert 1 galaxies (NLSy1s) are a well established class of γ -ray sources, showing the presence of a jet like the more common flat-spectrum radio quasars. The evidence of γ -ray emission poses the issue of the location of the γ -ray emitting zone and of the contribution of the γ - γ absorption within the broad-line region (BLR), since such objects have been detected by Fermi-LAT in the

  • Revisiting the 2PN Pericenter Precession in View of Possible Future Measurements
    Universe (IF 2.165) Pub Date : 2020-04-13
    Lorenzo Iorio

    At the second post-Newtonian (2PN) order, the secular pericenter precession ω ˙ 2 PN of either a full two-body system made of well-detached non-rotating monopole masses of comparable size and a restricted two-body system composed of a point particle orbiting a fixed central mass have been analytically computed so far with a variety of approaches. We offer our contribution by analytically computing

  • Present and Future Contributions of Reactor Experiments to Mass Ordering and Neutrino Oscillation Studies
    Universe (IF 2.165) Pub Date : 2020-04-08
    Vito Antonelli; Lino Miramonti; Gioacchino Ranucci

    After a long a glorious history, marked by the first direct proofs of neutrino existence and of the mixing between the first and third neutrino generations, the reactor antineutrino experiments are still well alive and will continue to give important contributions to the development of elementary particle physics and astrophysics. In parallel to the SBL (short baseline) experiments, that will be dedicated

  • Comparison of Strain Effect between Aluminum and Palladium Gated MOS Quantum Dot Systems
    Universe (IF 2.165) Pub Date : 2020-04-06
    Brian Chi Ho Mooy; Kuan Yen Tan; Nai Shyan Lai

    As nano-scale metal-oxide-semiconductor devices are cooled to temperatures below 1 K, detrimental effects due to unintentional dots become apparent. The reproducibility of the location of these unintentional dots suggests that there are other mechanisms in play, such as mechanical strains in the semiconductor introduced by metallic gates. Here, we investigate the formation of strain-induced dots on

  • Quantum Cosmology of Fab Four John Theory with Conformable Fractional Derivative
    Universe (IF 2.165) Pub Date : 2020-03-31
    Isaac Torres; Júlio César Fabris; Oliver Fabio Piattella; Antônio Brasil Batista

    We study a quantization via fractional derivative of a nonminimal derivative coupling cosmological theory, namely, the Fab Four John theory. Its Hamiltonian version presents the issue of fractional powers in the momenta. That problem is solved here by the application of the so-called conformable fractional derivative. This leads to a Wheeler–DeWitt equation of second order, showing that a Bohm–de Broglie

  • Model Independent Diagnostics in Interacting Dark Energy Models
    Universe (IF 2.165) Pub Date : 2020-03-30
    Ying Jiang; Zhongxu Han; Qian Zhang; Weiqiang Yang; Yabo Wu; Jinyang Li; Han Lou; Chenchen Zhao; Yan Wang

    In this paper, we have explored non-gravitational interaction dark energy model between dark energy and cold dark matter (CDM). The main purpose of this work is to explore the deviations from Λ C D M and to distinguish the evolution trajectory of the interaction dark energy model with different parameters. Six forms of interaction were focused on. We have analyzed the deceleration parameters of the

  • Stable Wormholes in the Background of an Exponential f(R) Gravity
    Universe (IF 2.165) Pub Date : 2020-03-26
    Ghulam Mustafa; Ibrar Hussain; M. Farasat Shamir

    The current paper is devoted to investigating wormhole solutions with an exponential gravity model in the background of f ( R ) theory. Spherically symmetric static spacetime geometry is chosen to explore wormhole solutions with anisotropic fluid source. The behavior of the traceless matter is studied by employing a particular equation of state to describe the important properties of the shape-function

  • Entropy and Energy of Static Spherically Symmetric Black Hole in f(R) Theory
    Universe (IF 2.165) Pub Date : 2020-03-20
    Yaoguang Zheng; Rong-Jia Yang

    We consider the new horizon first law in f ( R ) theory. We derive the general formulas to computed the entropy and energy for static spherically symmetric black hole. For applications, some nontrivial solutions in some popular f ( R ) theories are investigated, the entropies and the energies of static spherically symmetric black holes in these models are first calculated.

  • The Scale-Invariant Vacuum (SIV) Theory: A Possible Origin of Dark Matter and Dark Energy
    Universe (IF 2.165) Pub Date : 2020-03-18
    Andre Maeder; Vesselin G. Gueorguiev

    The Scale Invariant Vacuum (SIV) theory rests on the basic hypothesis that the macroscopic empty space is scale invariant. This hypothesis is applied in the context of the Integrable Weyl Geometry, where it leads to considerable simplifications in the scale covariant cosmological equations. After an initial explosion and a phase of braking, the cosmological models show a continuous acceleration of

  • Revisiting the Fraction of Radio-Loud Narrow Line Seyfert 1 Galaxies with LoTSS DR1
    Universe (IF 2.165) Pub Date : 2020-03-18
    Xu-Liang Fan

    Radio-Loud narrow-line Seyfert 1 galaxies (NLS1s), especially the extremely radio-loud ones, are widely accepted as the jetted versions of NLS1s. We explore the radio-loud fraction for NLS1s with recently released LoTSS DR1 at 150 MHz. The radio detection rate is about 28% for LoTSS DR1. The radio detected NLS1s have lower redshift than the non-detected ones. Moreover, the 150 MHz radio luminosities

  • Magnetized Particle Motion around Black Holes in Conformal Gravity: Can Magnetic Interaction Mimic Spin of Black Holes?
    Universe (IF 2.165) Pub Date : 2020-03-17
    Kamoliddin Haydarov; Ahmadjon Abdujabbarov; Javlon Rayimbaev; Bobomurat Ahmedov

    Magnetized particle motion around black holes in conformal gravity immersed in asymptotically uniform magnetic field has been studied. We have also analyzed the behavior of magnetic fields near the horizon of the black hole in conformal gravity and shown that with the increase of conformal parameters L and N the value of angular component of magnetic field at the stellar surface decreases. The maximum

  • Quantum Black Holes in the Sky
    Universe (IF 2.165) Pub Date : 2020-03-10
    Jahed Abedi; Niayesh Afshordi; Naritaka Oshita; Qingwen Wang

    Black Holes are possibly the most enigmatic objects in our universe. From their detection in gravitational waves upon their mergers, to their snapshot eating at the centres of galaxies, black hole astrophysics has undergone an observational renaissance in the past four years. Nevertheless, they remain active playgrounds for strong gravity and quantum effects, where novel aspects of the elusive theory

  • Evolution of Quasiperiodic Structures in a Non-Ideal Hydrodynamic Description of Phase Transitions
    Universe (IF 2.165) Pub Date : 2020-03-07
    D. N. Voskresensky

    Various phase transitions could have taken place in the early universe, and may occur in the course of heavy-ion collisions and supernova explosions, in proto-neutron stars, in cold compact stars, and in the condensed matter at terrestrial conditions. Most generally, the dynamics of the density and temperature at first- and second-order phase transitions can be described with the help of the equations

  • Exploring Light Sterile Neutrinos at Long Baseline Experiments: A Review
    Universe (IF 2.165) Pub Date : 2020-03-07
    Antonio Palazzo

    Several anomalies observed in short-baseline neutrino experiments suggest the existence of new light sterile neutrino species. In this review, we describe the potential role of long-baseline experiments in the searches of sterile neutrino properties and, in particular, the new CP-violation phases that appear in the enlarged 3 + 1 scheme. We also assess the impact of light sterile states on the discovery

  • Curvature Spinors in Locally Inertial Frame and the Relations with Sedenion
    Universe (IF 2.165) Pub Date : 2020-03-06
    In Ki Hong; Choong Sun Kim; Gyung Hyun Min

    In the 2-spinor formalism, the gravity can be dealt with curvature spinors with four spinor indices. Here we show a new effective method to express the components of curvature spinors in the rank-2 4 × 4 tensor representation for the gravity in a locally inertial frame. In the process we have developed a few manipulating techniques, through which the roles of each component of Riemann curvature tensor

  • Deformed General Relativity and Quantum Black Holes Interior
    Universe (IF 2.165) Pub Date : 2020-03-04
    Denis Arruga; Jibril Ben Achour; Karim Noui

    Effective models of black holes interior have led to several proposals for regular black holes. In the so-called polymer models, based on effective deformations of the phase space of spherically symmetric general relativity in vacuum, one considers a deformed Hamiltonian constraint while keeping a non-deformed vectorial constraint, leading under some conditions to a notion of deformed covariance. In

  • On the Solution of the Schrödinger Equation with Position-Dependent Mass
    Universe (IF 2.165) Pub Date : 2020-03-04
    Mehmet Sezgin

    We have considered the Iwasawa and Gauss decompositions for the Lie group SL(2,R). According to these decompositions, the Casimir operators of the group and the Hamiltonians with position-dependent mass were expressed. Then, the unbound state solutions of the Schrödinger equations with position-dependent mass were given.

  • Neutrino Oscillations and Lorentz Invariance Violation
    Universe (IF 2.165) Pub Date : 2020-02-27
    Marco Danilo Claudio Torri

    This work explores the possibility of resorting to neutrino phenomenology to detect evidence of new physics, caused by the residual signals of the supposed quantum structure of spacetime. In particular, this work investigates the effects on neutrino oscillations and mass hierarchy detection, predicted by models that violate Lorentz invariance, preserving the spacetime isotropy and homogeneity. Neutrino

  • Critical Evaluation of Common Claims in Loop Quantum Cosmology
    Universe (IF 2.165) Pub Date : 2020-02-26
    Martin Bojowald

    A large number of models have been analyzed in loop quantum cosmology, using mainly minisuperspace constructions and perturbations. At the same time, general physics principles from effective field theory and covariance have often been ignored. A consistent introduction of these ingredients requires substantial modifications of existing scenarios. As a consequence, none of the broader claims made mainly

  • Bifurcation Analysis and Periodic Solutions of the HD 191408 System with Triaxial and Radiative Perturbations
    Universe (IF 2.165) Pub Date : 2020-02-22
    Fabao Gao; Ruifang Wang

    The nonlinear orbital dynamics of a class of the perturbed restricted three-body problem is studied. The two primaries considered here refer to the binary system HD 191408. The third particle moves under the gravity of the binary system, whose triaxial rate and radiation factor are also considered. Based on the dynamic governing equation of the third particle in the binary HD 191408 system, the motion

  • Gravitoelectromagnetism, Solar System Tests, and Weak-Field Solutions in f (T,B) Gravity with Observational Constraints
    Universe (IF 2.165) Pub Date : 2020-02-18
    Gabriel Farrugia; Jackson Levi Said; Andrew Finch

    Gravitomagnetism characterizes phenomena in the weak-field limit within the context of rotating systems. These are mainly manifested in the geodetic and Lense-Thirring effects. The geodetic effect describes the precession of the spin of a gyroscope in orbit about a massive static central object, while the Lense-Thirring effect expresses the analogous effect for the precession of the orbit about a rotating

  • Squeezing of Primordial Gravitational Waves as Quantum Discord
    Universe (IF 2.165) Pub Date : 2020-02-15
    Akira Matsumura; Yasusada Nambu

    We investigate the squeezing of primordial gravitational waves (PGWs) in terms of quantum discord. We construct a classical state of PGWs without quantum discord and compare it with the Bunch–Davies vacuum. Then it is shown that the oscillatory behavior of the angular-power spectrum of the cosmic microwave background (CMB) fluctuations induced by PGWs can be the signature of the quantum discord of

  • Three-Flavor Oscillations with Accelerator Neutrino Beams
    Universe (IF 2.165) Pub Date : 2020-02-11
    Mauro Mezzetto; Francesco Terranova

    The three-flavor neutrino oscillation paradigm is well established in particle physics thanks to the crucial contribution of accelerator neutrino beam experiments. In this paper, we review the most important contributions of these experiments to the physics of massive neutrinos after the discovery of θ 13 and future perspectives in such a lively field of research. Special emphasis is given to the technical

  • Measuring Electromagnetic Fields in Rotating Frames of Reference
    Universe (IF 2.165) Pub Date : 2020-02-11
    Clive C. Speake; Antonello Ortolan

    We review the problem of transforming electromagnetic fields between inertial and rotating reference frames. We compare the method of straightforward tensor coordinate transformations adopted by Schiff in his well-known paper of 1939 with the method of Orthogonal Tetrads (OT) that was applied to this problem in 1964 by Irvine. Although both methods are mathematically rigorous, the transformed fields

  • Neutrino Telescopes and High-Energy Cosmic Neutrinos
    Universe (IF 2.165) Pub Date : 2020-02-10
    Andrea Palladino; Maurizio Spurio; Francesco Vissani

    In this review paper, we present the main aspects of high-energy cosmic neutrino astrophysics. We begin by describing the generic expectations for cosmic neutrinos, including the effects of propagation from their sources to the detectors. Then we introduce the operating principles of current neutrino telescopes, and examine the main features (topologies) of the observable events. After a discussion

  • Oscillating Neutrinos and Majorana Neutrino Masses
    Universe (IF 2.165) Pub Date : 2020-02-06
    Harald Fritzsch

    We discuss the mass matrices with texture zeros for the quarks and leptons. The flavor mixing angles for the quarks are functions of the quark masses and can be calculated. The results agree with the experimental data. The texture zero mass matrices for the leptons and the see-saw mechanism are used to derive relations between the matrix elements of the lepton mixing matrix and the ratios of the neutrino

  • A Table-Top Pilot Experiment for Narrow Mass Range Light Cold Dark Matter Particle Searches
    Universe (IF 2.165) Pub Date : 2020-02-03
    Masroor H. S. Bukhari

    This report presents the detection framework and a proposal for a pilot table-top experiment (supported by simulations and preliminary test results) for adoption into narrow mass range light Cold Dark Matter (CDM) searches, specifically for axions or Axion-Like Particles (ALPs) in a resonant cavity-based scheme. The novelty of this proposal lies in an attempt to concentrate searches corresponding to

  • Rotating Disc around a Schwarzschild Black Hole
    Universe (IF 2.165) Pub Date : 2020-02-03
    Oldřich Semerák; Pavel Čížek

    A stationary and axisymmetric (in fact circular) metric is reviewed which describes the first-order perturbation of a Schwarzschild black-hole space-time due to a rotating finite thin disc encircling the hole symmetrically. The key Green functions of the problem (corresponding to an infinitesimally thin ring)—the one for the gravitational potential and the one for the dragging angular velocity—were

  • Influence of Cosmic Repulsion and Magnetic Fields on Accretion Disks Rotating around Kerr Black Holes
    Universe (IF 2.165) Pub Date : 2020-01-29
    Zdeněk Stuchlík; Martin Kološ; Jiří Kovář; Petr Slaný; Arman Tursunov

    We present a review of the influence of cosmic repulsion and external magnetic fields on accretion disks rotating around rotating black holes and on jets associated with these rotating configurations. We consider both geometrically thin and thick disks. We show that the vacuum energy represented by the relic cosmological constant strongly limits extension of the accretion disks that is for supermassive

  • Black Holes and Wormholes in Extended Gravity
    Universe (IF 2.165) Pub Date : 2020-01-27
    Stanislav Alexeyev; Maxim Sendyuk

    We discuss black hole type solutions and wormhole type ones in the effective gravity models. Such models appear during the attempts to construct the quantum theory of gravity. The mentioned solutions, being, mostly, the perturbative generalisations of well-known ones in general relativity, carry out additional set of parameters and, therefore could help, for example, in the studying of the last stages

  • Rotation and Spin and Position Operators in Relativistic Gravity and Quantum Electrodynamics
    Universe (IF 2.165) Pub Date : 2020-01-26
    Robert F. O’Connell

    First, we examine how spin is treated in special relativity and the necessity of introducing spin supplementary conditions (SSC) and how they are related to the choice of a center-of-mass of a spinning particle. Next, we discuss quantum electrodynamics and the Foldy–Wouthuysen transformation which we note is a position operator identical to the Pryce–Newton–Wigner position operator. The classical version

  • Black Hole Evaporation: A Perspective from Loop Quantum Gravity
    Universe (IF 2.165) Pub Date : 2020-01-24
    Abhay Ashtekar

    A personal perspective on the black hole evaporation process is presented using, as guidelines, inputs from: (i) loop quantum gravity, (ii) simplified models where concrete results have been obtained, and, (iii) semi-classical quantum general relativity. On the one hand, the final picture is conservative in that there are concrete results that support each stage of the argument, and there are no large

  • Curvature Invariants for Charged and Rotating Black Holes
    Universe (IF 2.165) Pub Date : 2020-01-24
    James Overduin; Max Coplan; Kielan Wilcomb; Richard Conn Henry

    Riemann curvature invariants are important in general relativity because they encode the geometrical properties of spacetime in a manifestly coordinate-invariant way. Fourteen such invariants are required to characterize four-dimensional spacetime in general, and Zakhary and McIntosh showed that as many as seventeen can be required in certain degenerate cases. We calculate explicit expressions for

  • Shadow Images of a Rotating Dyonic Black Hole with a Global Monopole Surrounded by Perfect Fluid
    Universe (IF 2.165) Pub Date : 2020-01-24
    Sumarna Haroon; Kimet Jusufi; Mubasher Jamil

    In this paper, we revisit the rotating global monopole metric and extend the metric to a rotating dyonic global monopole in the presence of a perfect fluid. We then show that the surface topology at the event horizon, related to the metric computed, is a 2-sphere using the Gauss-Bonnet theorem. By choosing ω = − 1 / 3 , 0 , 1 / 3 we investigate the effect of dark matter, dust and radiation on the silhouette

  • Measuring Gravity at Cosmological Scales
    Universe (IF 2.165) Pub Date : 2020-01-22
    Luca Amendola; Dario Bettoni; Ana Marta Pinho; Santiago Casas

    This review is a pedagogical introduction to models of gravity and how they are constrained through cosmological observations. We focus on the Horndeski scalar-tensor theory and on the quantities that can be measured with a minimum of assumptions. Alternatives or extensions of general relativity have been proposed ever since its early years. Because of the Lovelock theorem, modifying gravity in four

  • Editorial for the Special Issue “Progress in Group Field Theory and Related Quantum Gravity Formalisms”
    Universe (IF 2.165) Pub Date : 2020-01-20
    Sylvain Carrozza; Steffen Gielen; Daniele Oriti

    This editorial introduces the Special Issue “Progress in Group Field Theory and Related Quantum Gravity Formalisms” which includes a number of research and review articles covering results in the group field theory (GFT) formalism for quantum gravity and in various neighbouring areas of quantum gravity research. We give a brief overview of the basic ideas of the GFT formalism, list some of its connections

  • Acknowledgement to Reviewers of Universe in 2019
    Universe (IF 2.165) Pub Date : 2020-01-20
    Universe Editorial Office

    Note: In lieu of an abstract, this is an excerpt from the first page. The editorial team greatly appreciates the reviewers who have dedicated their considerable time and expertise to the journal’s rigorous editorial process over the past 12 months, regardless of whether the papers are finally published or not [...]

  • Post-Editorial of “The Multiverse” Special Volume
    Universe (IF 2.165) Pub Date : 2020-01-20
    Ana Alonso-Serrano; Mariusz P. Da̧browski; Thomas Naumann

    A succesful series of papers devoted to various aspects of an idea of the Multiverse have been gathered together and presented to the readers. In this post-editorial we briefly challenge the content referring to the main issues dealt with by the Authors. We hope that this will inspire other investigators for designing future tests which could make this very notion of the Multiverse falsifiable.

  • Effects of Atomic-Scale Electron Density Profile and a Fast and Efficient Iteration Algorithm for Matter Effect of Neutrino Oscillation
    Universe (IF 2.165) Pub Date : 2020-01-18
    Mihai Horoi; Adam Zettel

    In a recent article, we noticed that the electron density in condensed matter exhibits large spikes close to the atomic nuclei. We showed that the peak magnitude of these spikes in the electron densities, 3–4 orders larger than the average electron plasma density in the Sun’s core, have no effect on the neutrino emission and absorption probabilities or on the neutrinoless double beta decay probability

  • Electrodynamics and Radiation from Rotating Neutron Star Magnetospheres
    Universe (IF 2.165) Pub Date : 2020-01-15
    Jérôme Pétri

    Neutron stars are compact objects rotating at high speed, up to a substantial fraction of the speed of light (up to 20% for millisecond pulsars) and possessing ultra-strong electromagnetic fields (close to and sometimes above the quantum critical field of 4.4 × 10 9 T ). Moreover, due to copious e ± pair creation within the magnetosphere, the relativistic plasma surrounding the star is forced into

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