scholarly journals Modified gravity over the linearized metric perturbation for two body dynamics

2021 ◽  
Author(s):  
Shubhen Biswas
Keyword(s):  
Binary System ◽  
Modified Gravity ◽  
Weak Field ◽  
New Paradigm ◽  
Newtonian Theory ◽  
Massive Black Hole ◽  
Body Dynamics ◽  
Remarkable Result ◽  
Self Force ◽  
Metric Perturbation

In this paper Modified gravity is studied over the weak field linearized metric perturbation in post-Minkowskian theory. This is a different aspect for studying the two body dynamics or binary system. Here despite of usual self force originated from the radiative backscattering of gravitational waves we are considering new paradigm of perturbation that is multiplicative approach. The new perturbed metric is determined over the multiplication of isolated background metric of curved space-time for two different massive sources in post-Newtonian theory. To verify the model and the theoretical result the binary system of Milky Way central super massive black hole to Sun is considered. The computation shows remarkable result without MOND for galactic flat rotation curve and solar rotational speed 249km/sec, obviously very good agreement with recent observed data.

scholarly journals Classical gravitational self-energy from double copy

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
Gabriel Luz Almeida ◽  
Stefano Foffa ◽  
Riccardo Sturani
Keyword(s):  
Gravitational Field ◽  
Binary System ◽  
The Self ◽  
Gravitational Coupling ◽  
Leading Order ◽  
Body System ◽  
Self Energy ◽  
Composite Systems ◽  
Body Dynamics ◽  
Double Copy

Abstract We apply the classical double copy to the calculation of self-energy of composite systems with multipolar coupling to gravitational field, obtaining next-to-leading order results in the gravitational coupling GN by generalizing color to kinematics replacement rules known in literature. When applied to the multipolar description of the two-body system, the self-energy diagrams studied in this work correspond to tail processes, whose physical interpretation is of radiation being emitted by the non-relativistic source, scattered by the curvature generated by the binary system and then re-absorbed by the same source. These processes contribute to the conservative two-body dynamics and the present work represents a decisive step towards the systematic use of double copy within the multipolar post-Minkowskian expansion.

scholarly journals External energy paradigm for black holes

2018 ◽  
Vol 33 (31) ◽  
pp. 1844025 ◽  
Author(s):  
Yuan K. Ha
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Gravitational Energy ◽  
Electrostatic Energy ◽  
New Paradigm ◽  
External Energy ◽  
Quantum Particles ◽  
Remarkable Result ◽  
The Moment ◽  
Constituent Mass

A new paradigm for black holes is introduced. It is known as the External Energy Paradigm. The paradigm asserts that all energies of a black hole are external quantities; they are absent inside the horizon. These energies include constituent mass, gravitational energy, electrostatic energy, rotational energy, heat energy, etc. As a result, quantum particles with charges and spins cannot exist inside the black hole. To validate the conclusion, we derive the moment of inertia of a Schwarzschild black hole and find that it is exactly equal to mass [Formula: see text] (Schwarzschild radius)2, indicating that all mass of the black hole is located at the horizon. This remarkable result can resolve several long-standing paradoxes in black hole theory; such as why entropy is proportional to area and not to volume, the singularity problem, the information loss problem and the perplexing firewall controversy.

A self-force approach to the two-body problem: The Green function method

2016 ◽  
Vol 25 (09) ◽  
pp. 1641015
Author(s):  
Marc Casals
Keyword(s):  
Black Hole ◽  
Green Function ◽  
The Self ◽  
Massive Black Hole ◽  
Green Function Method ◽  
Two Body Problem ◽  
Black Hole Spacetime ◽  
Novel Method ◽  
The Green Function ◽  
Self Force

The inspiral of a stellar-mass astrophysical object into a massive black hole may be modeled within perturbation theory of General Relativity via the so-called self-force. In this paper, we present a novel method for the calculation of the self-force which is based on the Green function (GF) of the wave equation satisfied by the field created by the smaller object. We review the results in [M. Casals, S. Dolan, A. C. Ottewill and B. Wardell, Phys. Rev. D 88 (2013) 044022; B. Wardell, C. R. Galley, A. Zenginoğlu, M. Casals, S. R. Dolan and A. C. Ottewill, Phys. Rev. D 89 (2014) 084021] on the GF and the self-force on a scalar charge (as a model for the gravitational case) moving on a Schwarzschild black hole spacetime. This GF method offers an appealing geometrical insight into the origin of the self-force and is a promising candidate for practical self-force calculations.

scholarly journals Linear stability of Einstein and de Sitter universes in the quadratic theory of modified gravity

2021 ◽  
Author(s):  
Mudhahir Al-Ajmi
Keyword(s):  
General Relativity ◽  
Linear Stability ◽  
Modified Gravity ◽  
De Sitter ◽  
Static Universe ◽  
Quadratic Theory ◽  
Sitter Universe ◽  
Einstein Static Universe ◽  
De Sitter Universe ◽  
Metric Perturbation

We consider the Einstein static and the de Sitter universe solutions and examine their instabilities in a subclass of quadratic modified theories for gravity. This modification proposed by Nash is an attempt to generalize general relativity. Interestingly, we discover that the Einstein static universe is unstable in the context of the modified gravity. In contrast to Einstein static universe, the de Sitter universe remains stable under metric perturbation up to the second order.

scholarly journals GRAVITATIONAL FIELD OF A GLOBAL MONOPOLE IN A MODIFIED GRAVITY

2011 ◽  
Vol 03 ◽  
pp. 446-454 ◽  
Author(s):  
T. R. P. CARAMÊS ◽  
E. R. BEZERRA DE MELLO ◽  
M. E. X. GUIMARÃES
Keyword(s):  
Gravitational Field ◽  
Modified Gravity ◽  
Field Approximation ◽  
Weak Field ◽  
Symmetric System ◽  
Radial Coordinate ◽  
Spherically Symmetric ◽  
Global Monopole ◽  
Field Equations ◽  
Metric Tensor

In this paper we analyze the gravitational field of a global monopole in the context of f(R) gravity. More precisely, we show that the field equations obtained are expressed in terms of [Formula: see text]. Since we are dealing with a spherically symmetric system, we assume that F(R) is a function of the radial coordinate only. Moreover, adopting the weak field approximation, we can provide all components of the metric tensor. A comparison with the corresponding results obtained in General Relativity and in the Brans-Dicke theory is also made.

scholarly journals Analytic approximations in GR and gravitational waves

2019 ◽  
Vol 28 (06) ◽  
pp. 1930011 ◽  
Author(s):  
Luc Blanchet
Keyword(s):  
Binary Systems ◽  
State Of The Art ◽  
Equations Of Motion ◽  
Slow Motion ◽  
Weak Field ◽  
Analytic Approximation ◽  
Compact Binary ◽  
Recent Developments ◽  
Motion Approximation ◽  
Self Force

Analytic approximation methods in general relativity play a very important role when analyzing the gravitational wave signals recently discovered by the LIGO and Virgo detectors. In this contribution, we present the state of the art and some recent developments in the famous post-Newtonian (PN) or slow-motion approximation, which has successfully computed the equations of motion and the early inspiral phase of compact binary systems. We discuss also some interesting interfaces between the PN and the gravitational self-force (GSF) approach based on black-hole perturbation theory, and between PN and the post-Minkowskian (PM) approximation, namely a nonlinearity expansion valid for weak field and possibly fast-moving sources.

scholarly journals Giant low-surface-brightness dwarf galaxy as a test bench for MOdified Gravity

2020 ◽  
Vol 493 (2) ◽  
pp. 2373-2376 ◽  
Author(s):  
Ivan de Martino
Keyword(s):  
Dark Matter ◽  
Modified Gravity ◽  
Dwarf Galaxy ◽  
Weak Field ◽  
Newtonian Potential ◽  
Modified Theories Of Gravity ◽  
Weak Field Limit ◽  
Low Surface Brightness ◽  
Standard Cosmological Model ◽  
Theories Of Gravity

ABSTRACT The lack of detection of supersymmetric particles is leading to look at alternative avenues for explaining dark matter’s effects. Among them, modified theories of gravity may play an important role accounting even for both dark components needed in the standard cosmological model. Scalar–tensor–vector gravity theory has been proposed to resolve the dark matter puzzle. Such a modified gravity model introduces, in its weak field limit, a Yukawa-like correction to the Newtonian potential, and is capable to explain most of the phenomenology related to dark matter at scale of galaxies and galaxy clusters. Nevertheless, some inconsistencies appear when studying systems that are supposed to be dark matter dominated such as dwarf galaxies. In this sense, Antlia II, an extremely diffuse galaxy which has been recently discovered in Gaia’s second data release, may serve to probe the aforementioned theory against the need for invoking dark matter. Our analysis shows several inconsistencies and leads to argue that MOdified Gravity may not be able to shed light on the intriguing nature of dark matter.

scholarly journals ON THE MOTION OF A TEST PARTICLE AROUND A GLOBAL MONOPOLE IN A MODIFIED GRAVITY

2012 ◽  
Vol 27 (30) ◽  
pp. 1250177 ◽  
Author(s):  
T. R. P. CARAMÊS ◽  
E. R. BEZERRA DE MELLO ◽  
M. E. X. GUIMARÃES
Keyword(s):  
Test Particle ◽  
Modified Gravity ◽  
Functional Form ◽  
Weak Field ◽  
Radial Coordinate ◽  
Spherically Symmetric ◽  
Global Monopole ◽  
Field Equations ◽  
Metric Tensor ◽  
Spherically Symmetric Metric

In this paper we suggest an approach to analyze the motion of a test particle in the spacetime of a global monopole within a f(R)-like modified gravity. The field equations are written in a simplified form in terms of [Formula: see text]. Since we are dealing with a spherically symmetric metric, we express F(R) as a function of the radial coordinate only, e.g., [Formula: see text]. So, the choice of a specific form for f(R) will be equivalent to adopt an Ansatz for [Formula: see text] . By choosing an explicit functional form for [Formula: see text], we obtain the weak field solutions for the metric tensor also compute the time-like geodesics and analyze the motion of a massive test particle. An interesting feature is an emerging attractive force exerted by the monopole on the particle.

scholarly journals New metric reconstruction scheme for gravitational self-force calculations

2021 ◽  
Author(s):  
Vahid Toomani ◽  
Peter J Zimmerman ◽  
Andrew Robert Clifford Spiers ◽  
Stefan Hollands ◽  
Adam Pound ◽  
...  
Keyword(s):  
Black Hole ◽  
Kerr Black Hole ◽  
Point Particle ◽  
Linear Perturbation ◽  
Field Equations ◽  
Reconstruction Procedure ◽  
Metric Reconstruction ◽  
Reconstruction Methods ◽  
Self Force ◽  
Metric Perturbation

Abstract Inspirals of stellar-mass objects into massive black holes will be important sources for the space-based gravitational-wave detector LISA. Modelling these systems requires calculating the metric perturbation due to a point particle orbiting a Kerr black hole. Currently, the linear perturbation is obtained with a metric reconstruction procedure that puts it in a “no-string” radiation gauge which is singular on a surface surrounding the central black hole. Calculating dynamical quantities in this gauge involves a subtle procedure of “gauge completion” as well as cancellations of very large numbers. The singularities in the gauge also lead to pathological field equations at second perturbative order. In this paper we re-analyze the point-particle problem in Kerr using the corrector-field reconstruction formalism of Green, Hollands, and Zimmerman (GHZ). We clarify the relationship between the GHZ formalism and previous reconstruction methods, showing that it provides a simple formula for the “gauge completion”. We then use it to develop a new method of computing the metric in a more regular gauge: a Teukolsky puncture scheme. This scheme should ameliorate the problem of large cancellations, and by constructing the linear metric perturbation in a sufficiently regular gauge, it should provide a first step toward second-order self-force calculations in Kerr. Our methods are developed in generality in Kerr, but we illustrate some key ideas and demonstrate our puncture scheme in the simple setting of a static particle in Minkowski spacetime.

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