scholarly journals On the Lambda-evolution of galaxy clusters

2020 ◽  
Vol 80 (1) ◽  
Author(s):  
V. G. Gurzadyan ◽  
A. A. Kocharyan ◽  
A. Stepanian
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Galaxy Clusters ◽  
Weak Field ◽  
Newtonian Gravity ◽  
Cosmological Time ◽  
The Common ◽  
Common Nature ◽  
The Difference ◽  
Evolutionary Paths

AbstractThe evolution of galaxy clusters can be affected by the repulsion described by the cosmological constant. This conclusion is reached within the modified weak-field General Relativity approach where the cosmological constant $$\varLambda $$Λ enables to describe the common nature of the dark matter and the dark energy. Geometrical methods of theory of dynamical systems and the Ricci curvature criterion are used to reveal the difference in the instability properties of galaxy clusters which determine their evolutionary paths. Namely, it is shown that the clusters determined by gravity with $$\varLambda $$Λ-repulsion tend to become even more unstable than those powered only by Newtonian gravity, the effect to be felt at cosmological time scales.

scholarly journals The invalidity of “negative mass” description of the dark sector

2019 ◽  
Vol 34 (35) ◽  
pp. 1975002
Author(s):  
A. Stepanian
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Observational Data ◽  
Weak Field ◽  
Dark Sector ◽  
Negative Mass ◽  
Negative Cosmological Constant ◽  
Viable Model

It is shown that the concept of “negative mass” introduced by Farnes [Astron. Astrophys. 620, A92 (2018)] to describe the dark sector within a unifying theory with the negative cosmological constant contradicts both the essence of the General Relativity (GR) and the available observational data. A viable model with modified weak-field GR is mentioned.

scholarly journals One gravitational potential or two? Forecasts and tests

2011 ◽  
Vol 369 (1957) ◽  
pp. 4947-4961 ◽  
Author(s):  
Edmund Bertschinger
Keyword(s):  
General Relativity ◽  
Gravitational Potential ◽  
Gravitational Lensing ◽  
Modified Gravity ◽  
Newtonian Potential ◽  
Newtonian Gravity ◽  
Peculiar Velocities ◽  
Modified Gravity Theories ◽  
Curvature Potential ◽  
The Difference

The metric of a perturbed Robertson–Walker space–time is characterized by three functions: a scale-factor giving the expansion history and two potentials that generalize the single potential of Newtonian gravity. The Newtonian potential induces peculiar velocities and, from these, the growth of matter fluctuations. Massless particles respond equally to the Newtonian potential and to a curvature potential. The difference of the two potentials, called the gravitational slip, is predicted to be very small in general relativity, but can be substantial in modified gravity theories. The two potentials can be measured, and gravity tested on cosmological scales, by combining weak gravitational lensing or the integrated Sachs–Wolfe effect with galaxy peculiar velocities or clustering.

On claims that general relativity differs from Newtonian physics for self-gravitating dusts in the low velocity, weak field limit

2015 ◽  
Vol 24 (08) ◽  
pp. 1550065 ◽  
Author(s):  
David R. Rowland
Keyword(s):  
General Relativity ◽  
Solar System ◽  
Relativistic Effects ◽  
Weak Field ◽  
Newtonian Gravity ◽  
Galactic Rotation ◽  
Low Velocity ◽  
Rotation Curves ◽  
Newtonian Physics ◽  
General Relativistic

Galaxy rotation curves are generally analyzed theoretically using Newtonian physics; however, two groups of authors have claimed that for self-gravitating dusts, general relativity (GR) makes significantly different predictions to Newtonian physics, even in the weak field, low velocity limit. One group has even gone so far as to claim that nonlinear general relativistic effects can explain flat galactic rotation curves without the need for cold dark matter. These claims seem to contradict the well-known fact that the weak field, low velocity, low pressure correspondence limit of GR is Newtonian gravity, as evidenced by solar system tests. Both groups of authors claim that their conclusions do not contradict this fact, with Cooperstock and Tieu arguing that the reason is that for the solar system, we have test particles orbiting a central gravitating body, whereas for a galaxy, each star is both an orbiting body and a contributor to the net gravitational field, and this supposedly makes a difference due to nonlinear general relativistic effects. Given the significance of these claims for analyses of the flat galactic rotation curve problem, this article compares the predictions of GR and Newtonian gravity for three cases of self-gravitating dusts for which the exact general relativistic solutions are known. These investigations reveal that GR and Newtonian gravity are in excellent agreement in the appropriate limits, thus supporting the conventional use of Newtonian physics to analyze galactic rotation curves. These analyses also reveal some sources of error in the referred to works.

scholarly journals The Impact of the Cosmological Constant on the Newtonian Gravity

2017 ◽  
Author(s):  
Engel Roza
Keyword(s):  
Cosmological Constant ◽  
Gravitational Force ◽  
Weak Field ◽  
Newtonian Gravity ◽  
Field Limit ◽  
Weak Field Limit ◽  
Spatial Periodicity ◽  
Spherical Isotropy ◽  
The One ◽  
The Impact

By solving the weak field limit of Einstein’s Field Equation including the Cosmological Constant, under the constraint of spherical isotropy, it is shown that, at large cosmological distance, the gravitational force exceeds the one that is predicted by Newton’s gravity law, such that it corresponds with Milgrom’s MOND hypothesis. However, the resulting prediction that, at extremely large distances, gravity with some spatial periodicity turns on-and-off into antigravity marks a decisive difference.

scholarly journals Restrictions on Extended Gravity at Galaxy Clusters Scales

2018 ◽  
Vol 191 ◽  
pp. 07008
Author(s):  
Stanislav Alexeyev ◽  
Boris Latosh ◽  
Vsevolod Echeistov
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Galaxy Clusters ◽  
Mass Range ◽  
Extended Gravity ◽  
Starobinsky Model ◽  
Observational Accuracy ◽  
Significant Difference ◽  
Accuracy Level

Following [1] we discuss the predictions of Starobinsky model of f(R)-gravity with vanishing cosmological constant at galaxy and galaxy clusters scales. As a result we demonstrate that at the current observational accuracy level there is no significant difference in cut-off radius values for Starobinsky model and general relativity (GR) in the mass range from 109MS un till galaxy clusters ones (1018MS un) that shows the good applicability of GR at these ranges.

scholarly journals HALO MODELS IN MODIFIED GRAVITY THEORIES WITH SELF-ACCELERATED EXPANSION

2011 ◽  
Vol 20 (12) ◽  
pp. 2383-2397 ◽  
Author(s):  
TATSUYA NARIKAWA ◽  
RAMPEI KIMURA ◽  
TATSUNOSUKE YANO ◽  
KAZUHIRO YAMAMOTO
Keyword(s):  
Gravity Model ◽  
Modified Gravity ◽  
Outer Region ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
Newtonian Gravity ◽  
Sphere Model ◽  
Modified Gravity Theories ◽  
The Common ◽  
The Difference

We investigate the structure of halos in the sDGP (self-accelerating branch of the Dvali–Gavadadze–Porrati braneworld gravity) model and the Galileon modified gravity model on the basis of the static and spherically symmetric solutions of the collisionless Boltzmann equation, which reduce to the singular isothermal sphere model and the King model in the limit of Newtonian gravity. The common feature of these halos is that the density of a halo in the outer region is larger (smaller) in the sDGP (Galileon) model, respectively, in comparison with Newtonian gravity. This comes from the suppression (enhancement) of the effective gravity at large distance in the sDGP (Galileon) model, respectively. However, the difference between these modified gravity models and Newtonian gravity only appears outside the halo due to the Vainshtein mechanism, which makes it difficult to distinguish between them. We also discuss the case in which the halo density profile is fixed independently of the gravity model for comparison between our results and previous work.

scholarly journals Torsion-induced gravitational $$\theta $$ term and gravitoelectromagnetism

2020 ◽  
Vol 80 (11) ◽  
Author(s):  
Athanasios Chatzistavrakidis ◽  
Georgios Karagiannis ◽  
Peter Schupp
Keyword(s):  
General Relativity ◽  
Topological Insulators ◽  
Mass Density ◽  
Weak Field ◽  
Riemann Tensor ◽  
Newton’S Law ◽  
The Common ◽  
Law Of Gravity ◽  
Physical Consequences ◽  
Nonlinear Gravity

AbstractMotivated by the analogy between a weak field expansion of general relativity and Maxwell’s laws of electrodynamics, we explore physical consequences of a parity violating $$\theta $$ θ term in gravitoelectromagnetism. This is distinct from the common gravitational $$\theta $$ θ term formed as a square of the Riemann tensor. Instead it appears as a product of the gravitoelectric and gravitomagnetic fields in the Lagrangian, similar to the Maxwellian $$\theta $$ θ term. We show that this sector can arise from a quadratic torsion term in nonlinear gravity. In analogy to the physics of topological insulators, the torsion-induced $$\theta $$ θ parameter can lead to excess mass density at the interface of regions where $$\theta $$ θ varies and consequently it generates a correction to Newton’s law of gravity. We discuss also an analogue of the Witten effect for gravitational dyons.

The power of weak-field GR gravity

2016 ◽  
Vol 25 (12) ◽  
pp. 1644017 ◽  
Author(s):  
F. I. Cooperstock
Keyword(s):  
General Relativity ◽  
Gravitational Field ◽  
Rotation Curve ◽  
Weak Field ◽  
Gps Tracking ◽  
Galactic Dynamics ◽  
Newtonian Gravity ◽  
Galactic Rotation ◽  
Compatibility Equation ◽  
Galactic Rotation Curve

While general relativity (GR) is our premier theory of gravity, galactic dynamics from the outset has been studied with Newtonian gravity (NG), guided by the long-held belief in the idea of the “Newtonian-limit” of GR. This maintains that when the gravitational field is weak and the velocities are nonrelativistic, NG is the appropriate theory, apart from small corrections at best (such as in GPS tracking). However, there are simple examples of phenomena where there is no NG counterpart. We present a particularly simple new example of the stark difference that NG and weak-field GR exhibit for a modified van Stockum source, which speaks to the flat galactic rotation curve problem. We note that the linear GR compatibility equation in the literature is incomplete. Its completion is vital for our case, leading to a stark contrast between GR and NG for totally flat van Stockum rotation curves.

scholarly journals The Impact of the Cosmological Constant on the Newtonian Gravity

2017 ◽  
Author(s):  
Engel Roza
Keyword(s):  
Cosmological Constant ◽  
Gravitational Force ◽  
Weak Field ◽  
Newtonian Gravity ◽  
Field Limit ◽  
Weak Field Limit ◽  
Spatial Periodicity ◽  
Spherical Isotropy ◽  
The One ◽  
The Impact

By solving the weak field limit of Einstein’s Field Equation including the Cosmological Constant, under the constraint of spherical isotropy, it is shown that, at large cosmological distance, the gravitational force exceeds the one that is predicted by Newton’s gravity law, such that it corresponds with Milgrom’s MOND hypothesis. However, the resulting prediction that, at extremely large distances, gravity with some spatial periodicity turns on-and-off into antigravity marks a decisive difference.

scholarly journals The Impact of the Cosmological Constant on the Newtonian Gravity

2018 ◽  
Author(s):  
Engel Roza
Keyword(s):  
Cosmological Constant ◽  
Gravitational Force ◽  
Weak Field ◽  
Newtonian Gravity ◽  
Field Limit ◽  
Weak Field Limit ◽  
Spatial Periodicity ◽  
Spherical Isotropy ◽  
The One ◽  
The Impact

By solving the weak field limit of Einstein’s Field Equation including the Cosmological Constant, under the constraint of spherical isotropy, it is shown that, at large cosmological distance, the gravitational force exceeds the one that is predicted by Newton’s gravity law, such that it corresponds with Milgrom’s MOND hypothesis.  However, the resulting prediction that, at extremely large distances, gravity with some spatial periodicity turns on-and-off into antigravity marks a decisive difference.

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